The Collaborative International Dictionary of English v.0.48:

Vinyl \Vi"nyl\, n. [L. vinum wine + -yl.] (Chem.)
   The hypothetical radical C2H3, regarded as the
   characteristic residue of ethylene and that related series of
   unsaturated hydrocarbons with which the allyl compounds are
   homologous.
   [1913 Webster]