Ethylidene /(?)/

E·thyl·i·dene

Ethylidene
  1. An unsymmetrical, divalent, hydrocarbon radical, C2H4 metameric with ethylene but written thus, CH3.CH= to distinguish it from the symmetrical ethylene, CH2=CH2. Its compounds are derived from aldehyde. Formerly called also ethidene. (Chem.)