1. [n]  a pedal that controls the throttle valve; "he stepped on the gas"
2. [n]  a fossil fuel in the gaseous state; used for cooking and heating homes
3. [n]  a state of excessive gas in the alimentary canal
4. [n]  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
5. [n]  a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines
6. [n]  a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely
7. [v]  show off
8. [v]  attack with gas; subject to gas fumes; "The despot gassed the rebellious tribes"

1. \Gas\ (g[a^]s), n.; pl. {Gases} (-[e^]z). [Invented by the
   chemist Van Helmont of Brussels, who died in 1644.]
   1. An a["e]riform fluid; -- a term used at first by chemists
      as synonymous with air, but since restricted to fluids
      supposed to be permanently elastic, as oxygen, hydrogen,
      etc., in distinction from vapors, as steam, which become
      liquid on a reduction of temperature. In present usage,
      since all of the supposed permanent gases have been
      liquified by cold and pressure, the term has resumed
      nearly its original signification, and is applied to any
      substance in the elastic or a["e]riform state.
   2. (Popular Usage)
      (a) A complex mixture of gases, of which the most
          important constituents are marsh gas, olefiant gas,
          and hydrogen, artificially produced by the destructive
          distillation of gas coal, or sometimes of peat, wood,
          oil, resin, etc. It gives a brilliant light when
          burned, and is the common gas used for illuminating
          purposes.
      (b) Laughing gas.
      (c) Any irrespirable a["e]riform fluid.
   Note: Gas is often used adjectively or in combination; as,
         gas fitter or gasfitter; gas meter or gas-meter, etc.
   {Air gas} (Chem.), a kind of gas made by forcing air through
      some volatile hydrocarbon, as the lighter petroleums. The
      air is so saturated with combustible vapor as to be a
      convenient illuminating and heating agent.
   {Gas battery} (Elec.), a form of voltaic battery, in which
      gases, especially hydrogen and oxygen, are the active
      agents.
   {Gas carbon}, {Gas coke}, etc. See under {Carbon}, {Coke},
      etc.
   {Gas coal}, a bituminous or hydrogenous coal yielding a high
      percentage of volatile matters, and therefore available
      for the manufacture of illuminating gas. --R. W. Raymond.
   {Gas engine}, an engine in which the motion of the piston is
      produced by the combustion or sudden production or
      expansion of gas; -- especially, an engine in which an
      explosive mixture of gas and air is forced into the
      working cylinder and ignited there by a gas flame or an
      electric spark.
   {Gas fitter}, one who lays pipes and puts up fixtures for
      gas.
   {Gas fitting}.
      (a) The occupation of a gas fitter.
      (b) pl. The appliances needed for the introduction of gas
          into a building, as meters, pipes, burners, etc.
   {Gas fixture}, a device for conveying illuminating or
      combustible gas from the pipe to the gas-burner,
      consisting of an appendage of cast, wrought, or drawn
      metal, with tubes upon which the burners, keys, etc., are
      adjusted.
   {Gas generator}, an apparatus in which gas is evolved; as:
      (a) a retort in which volatile hydrocarbons are evolved by
          heat;
      (b) a machine in which air is saturated with the vapor of
          liquid hydrocarbon; a carburetor;
      (c) a machine for the production of carbonic acid gas, for
          a["e]rating water, bread, etc. --Knight.
   {Gas jet}, a flame of illuminating gas.
   {Gas machine}, an apparatus for carbureting air for use as
      illuminating gas.
   {Gas meter}, an instrument for recording the quantity of gas
      consumed in a given time, at a particular place.
   {Gas retort}, a retort which contains the coal and other
      materials, and in which the gas is generated, in the
      manufacture of gas.
   {Gas stove}, a stove for cooking or other purposes, heated by
      gas.
   {Gas tar}, coal tar.
   {Gas trap}, a drain trap; a sewer trap. See 4th {Trap}, 5.
   {Gas washer} (Gas Works), an apparatus within which gas from
      the condenser is brought in contact with a falling stream
      of water, to precipitate the tar remaining in it.
      --Knight.
   {Gas water}, water through which gas has been passed for
      purification; -- called also {gas liquor} and {ammoniacal
      water}, and used for the manufacture of sal ammoniac,
      carbonate of ammonia, and Prussian blue. --Tomlinson.
   {Gas well}, a deep boring, from which natural gas is
      discharged. --Raymond.
   {Gas works}, a manufactory of gas, with all the machinery and
      appurtenances; a place where gas is generated for lighting
      cities.
   {Laughing gas}. See under {Laughing}.
   {Marsh gas} (Chem.), a light, combustible, gaseous
      hydrocarbon, {CH4}, produced artificially by the dry
      distillation of many organic substances, and occurring as
      a natural product of decomposition in stagnant pools,
      whence its name. It is an abundant ingredient of ordinary
      illuminating gas, and is the first member of the paraffin
      series. Called also {methane}, and in coal mines, {fire
      damp}.
   {Natural gas}, gas obtained from wells, etc., in
      Pennsylvania, Ohio, and elsewhere, and largely used for
      fuel and illuminating purposes. It is chiefly derived from
      the Coal Measures.
   {Olefiant gas} (Chem.). See {Ethylene}.
   {Water gas} (Chem.), a kind of gas made by forcing steam over
      glowing coals, whereby there results a mixture of hydrogen
      and carbon monoxide. This gives a gas of intense heating
      power, but destitute of light-giving properties, and which
      is charged by passing through some volatile hydrocarbon,
      as gasoline.
   

2. \Gas\, v. t. [imp. & p. p. {Gassed}; p. pr. & vb. n.
   {Gassing}.]
   1. (Textiles) To singe, as in a gas flame, so as to remove
      loose fibers; as, to gas thread.
   2. To impregnate with gas; as, to gas lime with chlorine in
      the manufacture of bleaching powder.
   

3. \Gas\, n.
   Gasoline. [Colloq.]
   

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