The Collaborative International Dictionary of English v.0.48:

Pentane \Pen"tane\, n. [See Penta-.] (Chem.)
   Any one of the three metameric hydrocarbons, C5H12, of the
   methane or paraffin series. They are colorless, volatile
   liquids, two of which occur in petroleum. So called because
   of the five carbon atoms in the molecule.
   [1913 Webster]