The Collaborative International Dictionary of English v.0.48:

Heptane \Hep"tane\, n. [Gr. "epta` seven.] (Chem.)
   Any one of several isometric hydrocarbons, C7H16, of the
   paraffin series (nine are possible, four are known); -- so
   called because the molecule has seven carbon atoms.
   Specifically, a colorless liquid, found as a constituent of
   petroleum, in the tar oil of cannel coal, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heptane
    n 1: a colorless volatile highly flammable liquid obtained from
         petroleum and used as an anesthetic or a solvent or in
         determining octane ratings