What is "ethylidene"

Ethylidene \E*thyl"i*dene\ (Chem.) 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.

n. (context organic chemistry especially in combination English) The divalent radical CH₃-CH= formally obtained by removing two hydrogen atoms from the same carbon atom of ethane