The Collaborative International Dictionary
Propidene
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.
Wiktionary
propidene
n. propylidene