Law has to do with rules and legal systems. If you live by the letter of the law, you follow society's guidelines to a T: you cross at the corner and always wait until the light is green.

A law is a rule that specifies what you can and can't do. Laws govern communities, countries, and even the world. Your town might have a leash law for dog owners, and international law prohibits throwing garbage off a boat. You can also refer to the police as "the law," as in "Don’t make me call the law." Law also refers to the entire legal system: We are all equal before the law (at least in theory).

Definitions of law
  1. noun
    the collection of rules imposed by authority
    “civilization presupposes respect for the law
    synonyms: jurisprudence
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    administrative law
    the body of rules and regulations and orders and decisions created by administrative agencies of government
    canon law, ecclesiastical law
    the body of codified laws governing the affairs of a Christian church
    civil law
    the body of laws established by a state or nation for its own regulation
    case law, common law, precedent
    a system of jurisprudence based on judicial precedents rather than statutory laws
    international law, law of nations
    the body of laws governing relations between nations
    law of the land
    a phrase used in the Magna Carta to refer to the then established law of the kingdom (as distinct from Roman or civil law); today it refers to fundamental principles of justice commensurate with due process
    martial law
    the body of law imposed by the military over civilian affairs (usually in time of war or civil crisis); overrides civil law
    commercial law, law merchant, mercantile law
    the body of rules applied to commercial transactions; derived from the practices of traders rather than from jurisprudence
    military law
    the body of laws and rules of conduct administered by military courts for the discipline, trial, and punishment of military personnel
    Law of Moses, Mosaic law
    the laws (beginning with the Ten Commandments) that God gave to the Israelites through Moses; it includes many rules of religious observance given in the first five books of the Old Testament (in Judaism these books are called the Torah)
    Islamic law, sharia, sharia law, shariah, shariah law
    the code of law derived from the Quran and from the teachings and example of Mohammed
    statutory law
    the body of laws created by legislative statutes
    securities law
    the body of laws governing the issuance and selling of securities
    tax law
    the body of laws governing taxation
    case law, common law, precedent
    (civil law) a law established by following earlier judicial decisions
    legislation, statute law
    law enacted by a legislative body
    admiralty law, marine law, maritime law
    the branch of international law that deals with territorial and international waters or with shipping or with ocean fishery etc.
    hudood, hudud
    Islamic laws stating the limits ordained by Allah and including the deterrent punishments for serious crimes
    type of:
    accumulation, aggregation, assemblage, collection
    several things grouped together or considered as a whole
  2. noun
    legal document setting forth rules governing a particular kind of activity
    “there is a law against kidnapping”
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    anti-drug law
    a law forbidding the sale or use of narcotic drugs
    RICO, RICO Act, Racketeer Influenced and Corrupt Organizations Act, anti-racketeering law
    law intended to eradicate organized crime by establishing strong sanctions and forfeiture provisions
    antitrust law, antitrust legislation
    law intended to promote free competition in the market place by outlawing monopolies
    statute of limitations
    a statute prescribing the time period during which legal action can be taken
    constitution, fundamental law, organic law
    law determining the fundamental political principles of a government
    public law
    a law affecting the public at large
    blue law
    a statute regulating work on Sundays
    blue sky law
    a state law regulating the sale of securities in an attempt to control the sale of securities in fraudulent enterprises
    gag law
    any law that limits freedom of the press
    homestead law
    a law conferring privileges on owners of homesteads
    poor law
    a law providing support for the poor
    Riot Act
    a former English law requiring mobs to disperse after a magistrate reads the law to them
    a law forbidding the sale of alcoholic beverages
    type of:
    instrument, legal document, legal instrument, official document
    (law) a document that states some contractual relationship or grants some right
  3. noun
    a rule or body of rules of conduct inherent in human nature and essential to or binding upon human society
    synonyms: natural law
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    divine law
    a law that is believed to come directly from God
    a basic truth or law or assumption
    sound law
    a law describing sound changes in the history of a language
    a guiding principle
    basic principle, basics, bedrock, fundamental principle, fundamentals
    principles from which other truths can be derived
    the principles that guide reasoning within a given field or situation
    pleasure principle, pleasure-pain principle, pleasure-unpleasure principle
    (psychoanalysis) the governing principle of the id; the principle that an infant seeks gratification and fails to distinguish fantasy from reality
    reality principle
    (psychoanalysis) the governing principle of the ego; the principle that as a child grows it becomes aware of the real environment and the need to accommodate to it
    the principle of revolt against constituted authority
    (physics) the maintenance of a certain quantities unchanged during chemical reactions or physical transformations
    Grimm's law
    a sound law relating German consonants and consonants in other Indo-European languages
    Verner's law
    a qualification of Grimm's law
    the ultimate principle of the universe
    type of:
    concept, conception, construct
    an abstract or general idea inferred or derived from specific instances
  4. noun
    a generalization that describes recurring facts or events in nature
    “the laws of thermodynamics”
    synonyms: law of nature
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    all-or-none law
    (neurophysiology) a nerve impulse resulting from a weak stimulus is just as strong as a nerve impulse resulting from a strong stimulus
    principle, rule
    a rule or law concerning a natural phenomenon or the function of a complex system
    Archimedes' principle, law of Archimedes
    (hydrostatics) the apparent loss in weight of a body immersed in a fluid is equal to the weight of the displaced fluid
    Avogadro's hypothesis, Avogadro's law
    the principle that equal volumes of all gases (given the same temperature and pressure) contain equal numbers of molecules
    Bernoulli's law, law of large numbers
    (statistics) law stating that a large number of items taken at random from a population will (on the average) have the population statistics
    Benford's law
    a law used by auditors to identify fictitious populations of numbers; applies to any population of numbers derived from other numbers
    Bose-Einstein statistics
    (physics) statistical law obeyed by a system of particles whose wave function is not changed when two particles are interchanged (the Pauli exclusion principle does not apply)
    Boyle's law, Mariotte's law
    the pressure of an ideal gas at constant temperature varies inversely with the volume
    Coulomb's Law
    a fundamental principle of electrostatics; the force of attraction or repulsion between two charged particles is directly proportional to the product of the charges and inversely proportional to the distance between them; principle also holds for magnetic poles
    Dalton's law, Dalton's law of partial pressures, law of partial pressures
    (chemistry and physics) law stating that the pressure exerted by a mixture of gases equals the sum of the partial pressures of the gases in the mixture; the pressure of a gas in a mixture equals the pressure it would exert if it occupied the same volume alone at the same temperature
    distribution law
    (chemistry) the total energy in an assembly of molecules is not distributed equally but is distributed around an average value according to a statistical distribution
    equilibrium law, law of chemical equilibrium
    (chemistry) the principle that (at chemical equilibrium) in a reversible reaction the ratio of the rate of the forward reaction to the rate of the reverse reaction is a constant for that reaction
    Fechner's law, Weber-Fechner law
    (psychophysics) the concept that the magnitude of a subjective sensation increases proportional to the logarithm of the stimulus intensity; based on early work by E. H. Weber
    Fermi-Dirac statistics
    (physics) law obeyed by a systems of particles whose wave function changes when two particles are interchanged (the Pauli exclusion principle applies)
    Charles's law, Gay-Lussac's law, law of volumes
    (physics) the density of an ideal gas at constant pressure varies inversely with the temperature
    Henry's law
    (chemistry) law formulated by the English chemist William Henry; the amount of a gas that will be absorbed by water increases as the gas pressure increases
    Hooke's law
    (physics) the principle that (within the elastic limit) the stress applied to a solid is proportional to the strain produced
    Hubble law, Hubble's law
    (astronomy) the generalization that the speed of recession of distant galaxies (the red shift) is proportional to their distance from the observer
    Kepler's law, Kepler's law of planetary motion
    (astronomy) one of three empirical laws of planetary motion stated by Johannes Kepler
    Kirchhoff's laws
    (physics) two laws governing electric networks in which steady currents flow: the sum of all the currents at a point is zero and the sum of the voltage gains and drops around any closed circuit is zero
    law of averages
    a law affirming that in the long run probabilities will determine performance
    law of constant proportion, law of definite proportions
    (chemistry) law stating that every pure substance always contains the same elements combined in the same proportions by weight
    law of diminishing returns
    a law affirming that to continue after a certain level of performance has been reached will result in a decline in effectiveness
    law of effect
    (psychology) the principle that behaviors are selected by their consequences; behavior having good consequences tends to be repeated whereas behavior that leads to bad consequences is not repeated
    law of equivalent proportions, law of reciprocal proportions
    (chemistry) law stating that the proportions in which two elements separately combine with a third element are also the proportions in which they combine together
    Newton's law of gravitation, law of gravitation
    (physics) the law that states any two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
    Dalton's law, law of multiple proportions
    (chemistry) law stating that when two elements can combine to form more than one compound the amounts of one of them that combines with a fixed amount of the other will exhibit a simple multiple relation
    law of mass action
    (chemistry) the law that states the following principle: the rate of a chemical reaction is directly proportional to the molecular concentrations of the reacting substances
    law of thermodynamics
    (physics) a law governing the relations between states of energy in a closed system
    Mendel's law
    (genetics) one of two principles of heredity formulated by Gregor Mendel on the basis of his experiments with plants; the principles were limited and modified by subsequent genetic research
    Newton's law, Newton's law of motion, law of motion
    one of three basic laws of classical mechanics
    Ohm's law
    electric current is directly proportional to voltage and inversely proportional to resistance; I = E/R
    Pascal's law, Pascal's law of fluid pressures
    pressure applied anywhere to a body of fluid causes a force to be transmitted equally in all directions; the force acts at right angles to any surface in contact with the fluid
    Pauli exclusion principle, exclusion principle
    no two electrons or protons or neutrons in a given system can be in states characterized by the same set of quantum numbers
    Mendeleev's law, periodic law
    (chemistry) the principle that chemical properties of the elements are periodic functions of their atomic numbers
    Planck's law
    (physics) the basis of quantum theory; the energy of electromagnetic waves is contained in indivisible quanta that have to be radiated or absorbed as a whole; the magnitude is proportional to frequency where the constant of proportionality is given by Planck's constant
    Planck's radiation law
    (physics) an equation that expresses the distribution of energy in the radiated spectrum of an ideal black body
    principle of relativity
    (physics) a universal law that states that the laws of mechanics are not affected by a uniform rectilinear motion of the system of coordinates to which they are referred
    Stevens' law, Stevens' power law, power law
    (psychophysics) the concept that the magnitude of a subjective sensation increases proportional to a power of the stimulus intensity
    Weber's law
    (psychophysics) the concept that a just-noticeable difference in a stimulus is proportional to the magnitude of the original stimulus
    Boltzmann distribution law, Maxwell-Boltzmann distribution law
    (physics) a law expressing the distribution of energy among the molecules of a gas in thermal equilibrium
    Gestalt law of organization, Gestalt principle of organization
    a principle of Gestalt psychology that identifies factors leading to particular forms of perceptual organization
    Kepler's first law
    a law stating that the orbit of each planet is an ellipse with the sun at one focus of the ellipse
    Kepler's second law, law of areas, law of equal areas
    a law concerning the speed at which planets travel; a line connecting a planet to the sun will sweep out equal areas in equal times
    Kepler's third law, harmonic law
    a law stating that the ratio of the square of the revolutionary period (in years) to the cube of the orbital axis (in astronomical units) is the same for all planets
    second law of thermodynamics
    a law stating that mechanical work can be derived from a body only when that body interacts with another at a lower temperature; any spontaneous process results in an increase of entropy
    third law of thermodynamics
    law stating that the entropy of a substance approaches zero as its temperature approaches absolute zero
    zeroth law of thermodynamics
    the law that if two bodies are in thermal equilibrium with a third body then the first two bodies are in thermal equilibrium with each other
    Le Chatelier principle, Le Chatelier's law, Le Chatelier's principle, Le Chatelier-Braun principle
    the principle that if any change is imposed on a system that is in equilibrium then the system tends to adjust to a new equilibrium counteracting the change
    Gresham's Law
    (economics) the principle that when two kinds of money having the same denominational value are in circulation the intrinsically more valuable money will be hoarded and the money of lower intrinsic value will circulate more freely until the intrinsically more valuable money is driven out of circulation; bad money drives out good; credited to Sir Thomas Gresham
    law of segregation
    members of a pair of homologous chromosomes separate during the formation of gametes and are distributed to different gametes so that every gamete receives only one member of the pair
    law of independent assortment
    each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random
    mass-energy equivalence
    (physics) the principle that a measured quantity of mass is equivalent (according to relativity theory) to a measured quantity of energy
    Naegele's rule
    rule for calculating an expected delivery date; subtract three months from the first day of the last menstrual period and add seven days to that date
    Newton's first law, Newton's first law of motion, first law of motion
    a body remains at rest or in motion with a constant velocity unless acted upon by an external force
    Newton's second law, Newton's second law of motion, second law of motion
    the rate of change of momentum is proportional to the imposed force and goes in the direction of the force
    Newton's third law, Newton's third law of motion, law of action and reaction, third law of motion
    action and reaction are equal and opposite
    Occam's Razor, Ockham's Razor, law of parsimony, principle of parsimony
    the principle that entities should not be multiplied needlessly; the simplest of two competing theories is to be preferred
    principle of equivalence
    (physics) the principle that an observer has no way of distinguishing whether his laboratory is in a uniform gravitational field or is in an accelerated frame of reference
    principle of liquid displacement
    (hydrostatics) the volume of a body immersed in a fluid is equal to the volume of the displaced fluid
    Huygens' principle of superposition, principle of superposition
    the displacement of any point due to the superposition of wave systems is equal to the sum of the displacements of the individual waves at that point
    principle of superposition, superposition, superposition principle
    (geology) the principle that in a series of stratified sedimentary rocks the lowest stratum is the oldest
    mass action, mass-action principle
    (neurology) the principle that the cortex of the brain operates as a coordinated system with large masses of neural tissue involved in all complex functioning
    localisation, localisation of function, localisation principle, localization, localization of function, localization principle
    (physiology) the principle that specific functions have relatively circumscribed locations in some particular part or organ of the body
    conservation of energy, first law of thermodynamics, law of conservation of energy
    the fundamental principle of physics that the total energy of an isolated system is constant despite internal changes
    type of:
    concept, conception, construct
    an abstract or general idea inferred or derived from specific instances
  5. noun
    the learned profession that is mastered by graduate study in a law school and that is responsible for the judicial system
    “he studied law at Yale”
    synonyms: practice of law
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    type of:
    learned profession
    one of the three professions traditionally believed to require advanced learning and high principles
  6. noun
    the branch of philosophy concerned with the law and the principles that lead courts to make the decisions they do
    synonyms: jurisprudence, legal philosophy
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    contract law
    that branch of jurisprudence that studies the rights and obligations of parties entering into contracts
    corporation law
    that branch of jurisprudence that studies the laws governing corporations
    matrimonial law
    that branch of jurisprudence that studies the laws governing matrimony
    patent law
    that branch of jurisprudence that studies the laws governing patents
    type of:
    the rational investigation of questions about existence and knowledge and ethics
  7. noun
    the force of policemen and officers
    “the law came looking for him”
    synonyms: constabulary, police, police force
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    European Law Enforcement Organisation, Europol
    police organization for the European Union; aims to improve effectiveness and cooperation among European police forces
    gendarmerie, gendarmery
    French police force; a group of gendarmes or gendarmes collectively
    Mutawa, Mutawa'een
    religious police in Saudi Arabia whose duty is to ensure strict adherence to established codes of conduct; offenders may be detained indefinitely; foreigners are not excluded
    Mounties, RCMP, Royal Canadian Mounted Police
    the federal police force of Canada
    New Scotland Yard, Scotland Yard
    the detective department of the metropolitan police force of London
    secret police
    a police force that operates in secrecy (usually against persons suspected of treason or sedition)
    SS, Schutzstaffel
    special police force in Nazi Germany founded as a personal bodyguard for Adolf Hitler in 1925; the SS administered the concentration camps
    posse, posse comitatus
    a temporary police force
    the secret state police in Nazi Germany; known for its terrorist methods
    type of:
    force, personnel
    group of people willing to obey orders
    law enforcement agency
    an agency responsible for insuring obedience to the laws
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