Matter can be found in solid, liquid, or gas form. The air you breathe in and the carbon dioxide you breathe out, are both examples of gas.

Gasoline is a kind of a gas that you use as car fuel, and when people say they need gas, usually this is the kind they're talking about. They're probably not talking about the digestive kind of gas that causes you to fart. There are poisons that can be released as gas, and you might hear about riot police somewhere gassing people: spraying them with harmful gas. Gas has no fixed shape and changes density easily.

Definitions of gas
  1. noun
    the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container
    synonyms: gaseous state
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    type of:
    state, state of matter
    (chemistry) the three traditional states of matter are solids (fixed shape and volume) and liquids (fixed volume and shaped by the container) and gases (filling the container)
  2. noun
    a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely
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    the envelope of gases surrounding any celestial body
    argonon, inert gas, noble gas
    any of the chemically inert gaseous elements of the helium group in the periodic table
    Cl, atomic number 17, chlorine
    a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)
    F, atomic number 9, fluorine
    a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite
    H, atomic number 1, hydrogen
    a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe
    N, atomic number 7, nitrogen
    a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues
    O, atomic number 8, oxygen
    a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust
    occurs in natural gas; used in the manufacture of rubber and fuels
    colorless gas found in natural gas and petroleum; used as a fuel
    a toxic mixture of gases (including carbon dioxide and carbon monoxide and nitrogen) after an explosion of firedamp in a mine
    a mixture of gases (mostly methane) that form in coal mines and become explosive when mixed with air
    a poisonous colorless flammable gas used in organic synthesis and to dope transistors and as a poison gas in warfare
    nitrogen dioxide
    a highly poisonous brown gas (NO2)
    nitric oxide
    a poisonous red-brown gas (NO)
    blow gas, blowing gas
    the gas leaving a generator during a blow period
    butene, butylene
    any of three isomeric hydrocarbons C4H8; all used in making synthetic rubbers
    a colorless toxic gas with a pungent almond odor; has been used in chemical warfare
    exhaust, exhaust fumes, fumes
    gases ejected from an engine as waste products
    a mixture of gases (especially oxygen) required for breathing; the stuff that the wind consists of
    compressed gas
    gas at a high pressure that can be used as a propellant
    ethene, ethylene
    a flammable colorless gaseous alkene; obtained from petroleum and natural gas and used in manufacturing many other chemicals; sometimes used as an anesthetic
    air gas, producer gas
    a gas made of carbon monoxide and hydrogen and nitrogen; made by passing air over hot coke
    formaldehyde, methanal
    a colorless poisonous gas; made by the oxidation of methanol
    greenhouse emission, greenhouse gas
    a gas that contributes to the greenhouse effect by absorbing infrared radiation
    bottled gas, liquefied petroleum gas
    hydrocarbon gases, usually propane or butane, kept under pressure
    water gas
    a mixture of hydrogen and carbon monoxide with small amounts of other gases; made by blowing steam over hot coke or coal
    ideal gas, perfect gas
    a hypothetical gas with molecules of negligible size that exert no intermolecular forces
    something that is inhaled
    a colorless odorless gas used as a fuel
    a colorless gas (O3) soluble in alkalis and cold water; a strong oxidizing agent; can be produced by electric discharge in oxygen or by the action of ultraviolet radiation on oxygen in the stratosphere (where it acts as a screen for ultraviolet radiation)
    a colorless poisonous gas that smells like new-mown hay; used in chemical warfare
    a colorless gas with a strong fishy smell; used as a pesticide
    poison gas
    a gas that is poisonous to breath or contact; used in chemical warfare
    propene, propylene
    a flammable gas obtained by cracking petroleum; used in organic synthesis
    a poisonous or foul smelling gas emitted from the earth
    sewer gas
    foul-smelling gas that forms in sewers
    the product of vaporization of a solid
    sulfur dioxide, sulphur dioxide
    a colorless toxic gas (SO2) that occurs in the gases from volcanoes; used in many manufacturing processes and present in industrial emissions; causes acid rain
    lachrymator, lacrimator, tear gas, teargas
    a gas that makes the eyes fill with tears but does not damage them; used in dispersing crowds
    the atmosphere and outer space as viewed from the earth
    CFC, chlorofluorocarbon
    a fluorocarbon with chlorine; formerly used as a refrigerant and as a propellant in aerosol cans
    CS gas, chlorobenzylidenemalononitrile
    a tear gas that is stronger than CN gas but wears off faster; can be deployed by grenades or cluster bombs; can cause skin burns and fatal pulmonary edema
    CN gas, chloroacetophenone
    a tear gas that is weaker than CS gas but lasts longer
    a radioactive isotope of hydrogen; atoms of tritium have three times the mass of ordinary hydrogen atoms
    Ar, argon, atomic number 18
    a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere
    a radioactive isotope of chlorine
    He, atomic number 2, helium
    a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)
    Kr, atomic number 36, krypton
    a colorless element that is one of the six inert gasses; occurs in trace amounts in air
    Ne, atomic number 10, neon
    a colorless odorless gaseous element that give a red glow in a vacuum tube; one of the six inert gasses; occurs in the air in small amounts
    an obsolete name for nitrogen
    LOX, liquid oxygen
    a bluish translucent magnetic liquid obtained by compressing gaseous oxygen and then cooling it below its boiling point; used as an oxidizer in rocket propellants
    Rn, atomic number 86, radon
    a radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health
    Xe, atomic number 54, xenon
    a colorless odorless inert gaseous element occurring in the earth's atmosphere in trace amounts
    used also in making gasoline components
    polybutene, polybutylene
    a polymer of butylene; used in lubricants and synthetic rubber
    CO2, carbon dioxide, carbonic acid gas
    a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis
    gaseous form of chloropicrin used as tear gas
    the air that is inhaled and exhaled in respiration
    hot air
    air that has been heated and tends to rise
    compressed air
    air at a pressure greater than that of the atmosphere
    TCE, trichloroethane, trichloroethylene
    a heavy colorless highly toxic liquid used as a solvent to clean electronic components and for dry cleaning and as a fumigant; causes cancer and liver and lung damage
    HFC, hydrofluorocarbon
    a fluorocarbon emitted as a by-product of industrial manufacturing
    liquid nitrogen
    nitrogen in a liquid state
    liquid air
    air in a liquid state
    marsh gas
    methane gas produced when vegetation decomposes in water
    bichloride of mercury, corrosive sublimate, mercuric chloride, mercury chloride
    a white poisonous soluble crystalline sublimate of mercury; used as a pesticide or antiseptic or wood preservative
    blistering agent, dichloroethyl sulfide, mustard agent, mustard gas, sulfur mustard
    a toxic war gas with sulfide based compounds that raises blisters and attacks the eyes and lungs; there is no known antidote
    nerve agent, nerve gas
    a toxic gas that is inhaled or absorbed through the skin and has harmful effects on the nervous and respiratory system
    PFC, perfluorocarbon
    a powerful greenhouse gas emitted during the production of aluminum
    sulfur hexafluoride, sulphur hexafluoride
    a colorless gas that is soluble in alcohol and ether; a powerful greenhouse gas widely used in the electrical utility industry
    type of:
    continuous amorphous matter that tends to flow and to conform to the outline of its container: a liquid or a gas
  3. noun
    a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines
    synonyms: gasolene, gasoline, petrol
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    leaded gasoline, leaded petrol
    gasoline treated with a lead compound to reduce motor knocks
    gasoline jelled with aluminum soaps; highly incendiary liquid used in fire bombs and flamethrowers
    unleaded gasoline, unleaded petrol
    gasoline that has not been treated with a lead compound
    type of:
    a substance that can be consumed to produce energy
    an organic compound containing only carbon and hydrogen
  4. noun
    a fossil fuel in the gaseous state; used for cooking and heating homes
    synonyms: natural gas
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    type of:
    fossil fuel
    fuel consisting of the remains of organisms preserved in rocks in the earth's crust with high carbon and hydrogen content
  5. noun
    a pedal that controls the throttle valve
    “he stepped on the gas
    synonyms: accelerator, accelerator pedal, gas pedal, gun, throttle
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    type of:
    foot lever, foot pedal, pedal, treadle
    a lever that is operated with the foot
  6. noun
    a state of excessive gas in the alimentary canal
    synonyms: flatulence, flatulency
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    type of:
    physical condition, physiological condition, physiological state
    the condition or state of the body or bodily functions
  7. verb
    attack with gas; subject to gas fumes
    “The despot gassed the rebellious tribes”
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    attack with teargas; subject to teargas fumes
    type of:
    assail, attack
    launch an attack or assault on; begin hostilities or start warfare with
  8. verb
    show off
    synonyms: blow, bluster, boast, brag, gasconade, shoot a line, swash, tout, vaunt
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    speak in a blustering or scornful manner
    crow, gloat, triumph
    dwell on with satisfaction
    congratulate, preen
    pride or congratulate (oneself) for an achievement
    type of:
    amplify, exaggerate, hyperbolise, hyperbolize, magnify, overdraw, overstate
    to enlarge beyond bounds or the truth
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