The Collaborative International Dictionary of English v.0.48:

Trope \Trope\, n. [L. tropus, Gr. ?, fr. ? to turn. See
   Torture, and cf. Trophy, Tropic, Troubadour,
   Trover.] (Rhet.)
   (a) The use of a word or expression in a different sense from
       that which properly belongs to it; the use of a word or
       expression as changed from the original signification to
       another, for the sake of giving life or emphasis to an
       idea; a figure of speech.
   (b) The word or expression so used.
       [1913 Webster]

             In his frequent, long, and tedious speeches, it has
             been said that a trope never passed his lips.
                                                  --Bancroft.
       [1913 Webster]

   Note: Tropes are chiefly of four kinds: metaphor, metonymy,
         synecdoche, and irony. Some authors make figures the
         genus, of which trope is a species; others make them
         different things, defining trope to be a change of
         sense, and figure to be any ornament, except what
         becomes so by such change.
         [1913 Webster]