The Collaborative International Dictionary of English v.0.48:

Propane \Pro"pane\, n. [Propyl + methane.] (Chem.)
   A heavy gaseous hydrocarbon, C3H8, of the paraffin series,
   occurring naturally dissolved in crude petroleum, and also
   made artificially; -- called also propyl hydride.
   [1913 Webster]

WordNet (r) 3.0 (2006):

propane
    n 1: colorless gas found in natural gas and petroleum; used as a
         fuel

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "propane":
   alcohol, benzine, briquette, burnable, butane, carbon, charcoal,
   coal, coke, combustible, dope, ethane, ethanol, fireball, firing,
   flammable, flammable material, fuel, fuel additive, fuel dope, gas,
   gas carbon, gasoline, heptane, hexane, inflammable,
   inflammable material, isooctane, jet fuel, kerosene, methane,
   methanol, natural gas, octane, oil, paraffin, peat, pentane,
   propellant, rocket fuel, turf