A rule is a regulation or direction for doing some particular activity. If you have a "no shoes" rule at your house, it means everyone has to take them off at the door.

Other than laws or conditions about what can't and can't be done, rules can be tried-and-true tips like a grammar rule about subject-verb agreement or a spelling rule about making a singular noun plural. Rule can also pertain to power — how someone handles it or how long it lasts, like the peaceful rule of a king whose rule lasted 50 years.

Definitions of rule
  1. noun
    prescribed guide for conduct or action
    synonyms: prescript
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    a rule adopted by an organization in order to regulate its own affairs and the behavior of its members
    an authoritative rule of conduct or procedure
    order, parliamentary law, parliamentary procedure, rules of order
    a body of rules followed by an assembly
    rule of evidence
    (law) a rule of law whereby any alleged matter of fact that is submitted for investigation at a judicial trial is established or disproved
    Miranda rule
    the rule that police (when interrogating you after an arrest) are obliged to warn you that anything you say may be used as evidence and to read you your constitutional rights (the right to a lawyer and the right to remain silent until advised by a lawyer)
    precept, principle
    rule of personal conduct
    golden rule
    any important rule
    (computer science) a rule stating that the quality of the output is a function of the quality of the input; put garbage in and you get garbage out
    an authoritative rule
    ordinance, regulation
    an authoritative rule
    a rule or especially body of rules or principles generally established as valid and fundamental in a field or art or philosophy
    rules governing socially acceptable behavior
    communications protocol, protocol
    (computer science) rules determining the format and transmission of data
    game law
    a regulation intended to manage or preserve game animals
    (parliament) a parliamentary procedure of demanding that a government official explain some act or policy
    best evidence rule
    a rule of evidence requiring that to prove the content of a writing or recording or photograph the original is required
    a rule of evidence whereby a person is barred from denying the truth of a fact that has already been settled
    exclusionary rule
    a rule that provides that otherwise admissible evidence cannot be used in a criminal trial if it was the result of illegal police conduct
    fruit of the poisonous tree
    a rule that once primary evidence is determined to have been illegally obtained any secondary evidence following from it may also not be used
    hearsay rule
    a rule that declares not admissible as evidence any statement other than that by a witness
    parol evidence rule
    a rule that oral evidence cannot be used to contradict the terms of a written contract
    res ipsa loquitur
    a rule of evidence whereby the negligence of an alleged wrongdoer can be inferred from the fact that the accident happened
    standing order
    a rule of order permanently in force
    higher law
    a principle that takes precedent over the laws of society
    moral principle
    the principle that conduct should be moral
    hypothetical imperative
    a principle stating the action required to attain a desired goal
    caveat emptor
    a commercial principle that without a warranty the buyer takes upon himself the risk of quality
    age limit
    regulation establishing the maximum age for doing something or holding some position
    the regulation of weights and measures of articles offered for sale
    speed limit
    regulation establishing the top speed permitted on a given road
    forms of ceremony and etiquette observed by diplomats and heads of state
    FTP, file transfer protocol
    protocol that allows users to copy files between their local system and any system they can reach on the network
    HTTP, hypertext transfer protocol
    a protocol (utilizing TCP) to transfer hypertext requests and information between servers and browsers
    MIDI, musical instrument digital interface
    a standard protocol for communication between electronic musical instruments and computers
    TCP, transmission control protocol
    a protocol developed for the internet to get data from one network device to another
    TCP/IP, transmission control protocol/internet protocol
    a set of protocols (including TCP) developed for the internet in the 1970s to get data from one network device to another
    a fine point of etiquette or petty formality
    closure, cloture, gag law, gag rule
    a rule for limiting or ending debate in a deliberative body
    point of order
    a question as to whether the current proceedings are allowed by parliamentary procedure
    res gestae
    rule of evidence that covers words that are so closely associated with an occurrence that the words are considered part of the occurrence and as such their report does not violate the hearsay rule
    previous question
    a motion calling for an immediate vote on the main question under discussion by a deliberative assembly
    type of:
    direction, instruction
    a message describing how something is to be done
  2. noun
    a principle or condition that customarily governs behavior
    “it was his rule to take a walk before breakfast”
    synonyms: regulation
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    limitation, restriction, stricture
    a principle that limits the extent of something
    guideline, guidepost, rule of thumb
    a rule or principle that provides guidance to appropriate behavior
    cy pres, cy pres doctrine, rule of cy pres
    a rule that when literal compliance is impossible the intention of a donor or testator should be carried out as nearly as possible
    working principle, working rule
    a rule that is adequate to permit work to be done
    a restriction of range or scope
    a limitation imposed on the variables of a proposition (as by the quantifiers `some' or `all' or `no')
    a rule or condition that limits freedom
    type of:
    concept, conception, construct
    an abstract or general idea inferred or derived from specific instances
  3. noun
    a basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct
    synonyms: principle, tenet
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    a fundamental principle or practice
    the bright positive masculine principle in Chinese dualistic cosmology
    the dark, negative feminine principle in Chinese dualistic cosmology
    feng shui
    rules in Chinese philosophy that govern spatial arrangement and orientation in relation to patterns of yin and yang and the flow of energy (qi); the favorable or unfavorable effects are taken into consideration in designing and siting buildings and graves and furniture
    pillar of Islam
    (Islam) one of the five religious obligations accepted by all Muslims
    type of:
    generalisation, generality, generalization
    an idea or conclusion having general application
  4. noun
    directions that define the way a game or sport is to be conducted
    “he knew the rules of chess”
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    ground rule
    (baseball) a special rule (as in baseball) dealing with situations that arise due to the nature of the playing grounds
    type of:
    direction, instruction
    a message describing how something is to be done
  5. noun
    any one of a systematic body of regulations defining the way of life of members of a religious order
    “the rule of St. Dominic”
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    type of:
    direction, instruction
    a message describing how something is to be done
  6. noun
    a rule or law concerning a natural phenomenon or the function of a complex system
    “the right-hand rule for inductive fields”
    synonyms: principle
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    Gestalt law of organization, Gestalt principle of organization
    a principle of Gestalt psychology that identifies factors leading to particular forms of perceptual organization
    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
    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
    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
    lateralisation, laterality, lateralization
    localization of function on either the right or left sides of the brain
    closure, law of closure
    a Gestalt principle of organization holding that there is an innate tendency to perceive incomplete objects as complete and to close or fill gaps and to perceive asymmetric stimuli as symmetric
    common fate, law of common fate
    a Gestalt principle of organization holding that aspects of perceptual field that move or function in a similar manner will be perceived as a unit
    continuation, good continuation, law of continuation
    a Gestalt principle of organization holding that there is an innate tendency to perceive a line as continuing its established direction
    law of proximity, proximity
    a Gestalt principle of organization holding that (other things being equal) objects or events that are near to one another (in space or time) are perceived as belonging together as a unit
    law of similarity, similarity
    a Gestalt principle of organization holding that (other things being equal) parts of a stimulus field that are similar to each other tend to be perceived as belonging together as a unit
    type of:
    law, law of nature
    a generalization that describes recurring facts or events in nature
  7. noun
    (linguistics) a rule describing (or prescribing) a linguistic practice
    synonyms: linguistic rule
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    linguistic universal, universal
    (linguistics) a grammatical rule (or other linguistic feature) that is found in all languages
    grammatical rule, rule of grammar
    a linguistic rule for the syntax of grammatical utterances
    morphological rule, rule of morphology
    a linguistic rule for the formation of words
    a rule describing the conversion of one syntactic structure into another related syntactic structure
    type of:
    concept, conception, construct
    an abstract or general idea inferred or derived from specific instances
  8. noun
    (mathematics) a standard procedure for solving a class of mathematical problems
    “he determined the upper bound with Descartes' rule of signs”
    synonyms: formula
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    a rule that describes how other rules should be used (as in AI)
    algorithm, algorithmic program, algorithmic rule
    a precise rule (or set of rules) specifying how to solve some problem
    heuristic, heuristic program, heuristic rule
    a commonsense rule (or set of rules) intended to increase the probability of solving some problem
    (mathematics) an expression such that each term is generated by repeating a particular mathematical operation
    sorting algorithm
    an algorithm for sorting a list
    stemmer, stemming algorithm
    an algorithm for removing inflectional and derivational endings in order to reduce word forms to a common stem
    lateral thinking
    a heuristic for solving problems; you try to look at the problem from many angles instead of tackling it head-on
    type of:
    procedure, process
    a particular course of action intended to achieve a result
  9. noun
    something regarded as a normative example
    “violence is the rule not the exception”
    synonyms: convention, formula, normal, pattern
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    (sociology) the conventions that embody the fundamental values of a group
    code of behavior, code of conduct
    a set of conventional principles and expectations that are considered binding on any person who is a member of a particular group
    a behavioral convention or pattern characteristic of all members of a particular culture or of all human beings
    courtly love
    (Middle Ages) a highly conventionalized code of conduct for lovers
    knight errantry
    (Middle Ages) the code of conduct observed by a knight errant who is wandering in search of deeds of chivalry
    code of correct conduct
    type of:
    knowledge of how something is usually done
  10. noun
    the duration of a monarch's or government's power
    “during the rule of Elizabeth”
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    the period from 1811-1820 when the Prince of Wales was regent during George III's periods of insanity
    the period of time during which a regent governs
    type of:
    continuance, duration
    the period of time during which something continues
  11. noun
    dominance or power through legal authority
    “the rule of Caesar”
    synonyms: dominion
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    the state of being paramount; the highest rank or authority
    British dominion over India (1757-1947)
    reign, sovereignty
    royal authority; the dominion of a monarch
    the position or authority of a suzerain
    scepter, sceptre
    the imperial authority symbolized by a scepter
    type of:
    ascendance, ascendancy, ascendence, ascendency, control, dominance
    the state that exists when one person or group has power over another
  12. verb
    decide with authority
    synonyms: decree
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    override, overrule, overthrow, overturn, reverse
    rule against
    rule in, rule out
    include or exclude by determining judicially or in agreement with rules
    type of:
    decide, determine, make up one's mind
    reach, make, or come to a decision about something
  13. verb
    decide on and make a declaration about
    synonyms: find
    feel, find
    come to believe on the basis of emotion, intuitions, or indefinite grounds
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    judge, label, pronounce
    pronounce judgment on
  14. verb
    exercise authority over; as of nations
    synonyms: govern
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    sit on the throne as a ruler
    govern badly
    rule as a dictator
    have sovereign power
    grind down, tyrannise, tyrannize
    rule a country as a tyrant
    type of:
    command, control
    exercise authoritative control or power over
  15. noun
    measuring stick consisting of a strip of wood or metal or plastic with a straight edge that is used for drawing straight lines and measuring lengths
    synonyms: ruler
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    carpenter's rule
    a rule used by a carpenter
    foot rule
    a ruler one foot long
    meterstick, metrestick
    a rule one meter long (usually marked off in centimeters and millimeters)
    yard measure, yardstick
    a ruler or tape that is three feet long
    type of:
    measure, measuring rod, measuring stick
    measuring instrument having a sequence of marks at regular intervals; used as a reference in making measurements
  16. verb
    mark or draw with a ruler
    rule the margins”
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    type of:
    represent by making a drawing of, as with a pencil, chalk, etc. on a surface
  17. verb
    be larger in number, quantity, power, status or importance
    synonyms: dominate, predominate, prevail, reign
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    prevail over
    be central or dominant
    outbalance, outweigh, overbalance, preponderate
    weigh more heavily
  18. verb
    keep in check
    rule one's temper”
    synonyms: harness, rein
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    type of:
    bound, confine, limit, restrain, restrict, throttle, trammel
    place limits on (extent or access)
  19. verb
    have an affinity with; of signs of the zodiac
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    type of:
    accompany, attach to, come with, go with
    be present or associated with an event or entity
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