Source : Webster's Revised Unabridged Dictionary (1913)

Propidene \Pro"pi*dene\, n. [Propyl + ethylidene.] (Chem.)
   The unsymmetrical hypothetical hydrocarbon radical,
   {CH3.CH2.CH}, analogous to ethylidene, and regarded as the
   type of certain derivatives of propane; -- called also
   {propylidene}.