The Collaborative International Dictionary of English v.0.48:

Simile \Sim"i*le\, n.; pl. Similes. [L., from similis. See
   Similar.] (Rhet.)
   A word or phrase by which anything is likened, in one or more
   of its aspects, to something else; a similitude; a poetical
   or imaginative comparison.
   [1913 Webster]

         A good swift simile, but something currish. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

simile
    n 1: a figure of speech that expresses a resemblance between
         things of different kinds (usually formed with `like' or
         `as')