The Collaborative International Dictionary of English v.0.48:

Ethyl \Eth"yl\, n. [Ether + -yl.] (Chem.)
   A monatomic, hydrocarbon radical, C2H5 of the paraffin
   series, forming the essential radical of ethane, and of
   common alcohol and ether.
   [1913 Webster]

   Ethyl aldehyde. (Chem.) See Aldehyde.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ethyl
    n 1: the univalent hydrocarbon radical C2H5 derived from ethane
         by the removal of one hydrogen atom [syn: ethyl, ethyl
         group, ethyl radical]