The Collaborative International Dictionary of English v.0.48:

Acetylene \A*cet"y*lene\, n. (Chem.)
   A gaseous compound of carbon and hydrogen, in the proportion
   of two atoms of the former to two of the latter. It is a
   colorless gas, with a peculiar, unpleasant odor, and is
   produced for use as an illuminating gas in a number of ways,
   but chiefly by the action of water on calcium carbide. Its
   light is very brilliant. --Watts.
   [1913 Webster] Ach

WordNet (r) 3.0 (2006):

acetylene
    n 1: a colorless flammable gas used chiefly in welding and in
         organic synthesis [syn: acetylene, ethyne, alkyne]