The Collaborative International Dictionary of English v.0.48:

Butane \Bu"tane\ (b[=u]"t[=a]n), n. [L. butyrum butter. See
   Butter.] (Chem.)
   An inflammable gaseous saturated hydrocarbon, C4H10, of the
   marsh gas, or paraffin, series.
   [1913 Webster]

WordNet (r) 3.0 (2006):

butane
    n 1: occurs in natural gas; used in the manufacture of rubber
         and fuels