The Collaborative International Dictionary of English v.0.48:

Ethenyl \Eth"e*nyl\, n. [Ethene + -yl.] (Chem.)
   (a) A trivalent hydrocarbon radical, CH3.C.
   (b) A univalent hydrocarbon radical of the ethylene series,
       CH2:CH; -- called also vinyl. See Vinyl.
       [1913 Webster]