Source : Webster's Revised Unabridged Dictionary (1913)

   {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.

Marsh \Marsh\, n. [OE. mersch, AS. mersc, fr. mere lake. See
   {Mere} pool, and cf. {Marish}, {Morass}.]
   A tract of soft wet land, commonly covered partially or
   wholly with water; a fen; a swamp; a morass. [Written also
   {marish}.]

   {Marsh asphodel} (Bot.), a plant ({Nartheeium ossifragum})
      with linear equitant leaves, and a raceme of small white
      flowers; -- called also {bog asphodel}.

   {Marsh cinquefoil} (Bot.), a plant ({Potentilla palustris})
      having purple flowers, and found growing in marshy places;
      marsh five-finger.

   {Marsh elder}. (Bot.)
   (a) The guelder-rose or cranberry tree ({Viburnum Opulus}).
   (b) In the United States, a composite shrub growing in salt
       marshes ({Iva frutescens}).

   {Marsh five-finger}. (Bot.) See {Marsh cinquefoil} (above).
      

   {Marsh gas}. (Chem.) See under {Gas}.

   {Marsh grass} (Bot.), a genus ({Spartina}) of coarse grasses
      growing in marshes; -- called also {cord grass}. The tall
      {S. cynosuroides} is not good for hay unless cut very
      young. The low {S. juncea} is a common component of salt
      hay.

   {Marsh harrier} (Zo["o]l.), a European hawk or harrier
      ({Circus [ae]ruginosus}); -- called also {marsh hawk},
      {moor hawk}, {moor buzzard}, {puttock}.

   {Marsh hawk}. (Zo["o]l.)
   (a) A hawk or harrier ({Circus cyaneus}), native of both
       America and Europe. The adults are bluish slate above,
       with a white rump. Called also {hen harrier}, and {mouse
       hawk}.
   (b) The marsh harrier.

   {Marsh hen} (Zo["o]l.), a rail; esp., {Rallus elegans} of
      fresh-water marshes, and {R. longirostris} of salt-water
      marshes.

   {Marsh mallow} (Bot.), a plant of the genus {Alth[ae]a} ( {A.
      officinalis}) common in marshes near the seashore, and
      whose root is much used in medicine as a demulcent.

   {Marsh marigold}. (Bot.) See in the Vocabulary.

   {Marsh pennywort} (Bot.), any plant of the umbelliferous
      genus {Hydrocotyle}; low herbs with roundish leaves,
      growing in wet places; -- called also {water pennywort}.
      

   {Marsh quail} (Zo["o]l.), the meadow lark.

   {Marsh rosemary} (Bot.), a plant of the genus {Statice} ({S.
      Limonium}), common in salt marshes. Its root is powerfully
      astringent, and is sometimes used in medicine. Called also
      {sea lavender}.

   {Marsh samphire} (Bot.), a plant ({Salicornia herbacea})
      found along seacoasts. See {Glasswort}.

   {Marsh St. John's-wort} (Bot.), an American herb ({Elodes
      Virginica}) with small opposite leaves and flesh-colored
      flowers.

   {Marsh tea}. (Bot.). Same as {Labrador tea}.

   {Marsh trefoil}. (Bot.) Same as {Buckbean}.

   {Marsh wren} (Zo["o]l.), any species of small American wrens
      of the genus {Cistothorus}, and allied genera. They
      chiefly inhabit salt marshes.

Source : WordNet®

marsh gas
     n : methane gas produced when vegetation decomposes in water