Source : Webster's Revised Unabridged Dictionary (1913)

Plum \Plum\, n. [AS. pl[=u]me, fr. L. prunum; akin to Gr. ?, ?.
   Cf. {Prune} a dried plum.]
   1. (Bot.) The edible drupaceous fruit of the {Prunus
      domestica}, and of several other species of {Prunus};
      also, the tree itself, usually called {plum tree}.

            The bullace, the damson, and the numerous varieties
            of plum, of our gardens, although growing into
            thornless trees, are believed to be varieties of the
            blackthorn, produced by long cultivation. --G.
                                                  Bentham.

Source : WordNet®

plum tree
     n : any of several trees producing edible oval smooth-skinned
         fruit with a single hard stone [syn: {plum}]