The Collaborative International Dictionary of English v.0.48:

Plum \Plum\, n. [AS. pl[=u]me, fr. L. prunum; akin to Gr. ?, ?.
   Cf. Prune a dried plum.]
   [1913 Webster]
   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.
      [1913 Webster]

            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.
      [1913 Webster]

   Note: Two or three hundred varieties of plums derived from
         the Prunus domestica are described; among them the
         greengage, the Orleans, the purple gage, or
         Reine Claude Violette, and the German prune, are
         some of the best known.
         [1913 Webster]

   Note: Among the true plums are;

   Beach plum, the Prunus maritima, and its crimson or
      purple globular drupes,

   Bullace plum. See Bullace.

   Chickasaw plum, the American Prunus Chicasa, and its
      round red drupes.

   Orleans plum, a dark reddish purple plum of medium size,
      much grown in England for sale in the markets.

   Wild plum of America, Prunus Americana, with red or
      yellow fruit, the original of the Iowa plum and several
      other varieties.
      [1913 Webster] Among plants called plum, but of other
      genera than Prunus, are;

   Australian plum, Cargillia arborea and Cargillia
      australis, of the same family with the persimmon.

   Blood plum, the West African H[ae]matostaphes Barteri.

   Cocoa plum, the Spanish nectarine. See under Nectarine.


   Date plum. See under Date.

   Gingerbread plum, the West African Parinarium
      macrophyllum.

   Gopher plum, the Ogeechee lime.

   Gray plum, Guinea plum. See under Guinea.

   Indian plum, several species of Flacourtia.
      [1913 Webster]

   2. A grape dried in the sun; a raisin.
      [1913 Webster]

   3. A handsome fortune or property; formerly, in cant
      language, the sum of [pounds]100,000 sterling; also, the
      person possessing it.
      [1913 Webster]

   4. Something likened to a plum in desirableness; a good or
      choice thing of its kind, as among appointments,
      positions, parts of a book, etc.; as, the mayor rewarded
      his cronies with cushy plums, requiring little work for
      handsome pay
      [Webster 1913 Suppl. +PJC]

   5. A color resembling that of a plum; a slightly grayish deep
      purple, varying somewhat in its red or blue tint.
      [PJC]

   Plum bird, Plum budder (Zool.), the European bullfinch.


   Plum gouger (Zool.), a weevil, or curculio (Coccotorus
      scutellaris), which destroys plums. It makes round holes
      in the pulp, for the reception of its eggs. The larva
      bores into the stone and eats the kernel.

   Plum weevil (Zool.), an American weevil which is very
      destructive to plums, nectarines, cherries, and many other
      stone fruits. It lays its eggs in crescent-shaped
      incisions made with its jaws. The larva lives upon the
      pulp around the stone. Called also turk, and plum
      curculio. See Illust. under Curculio.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Prune \Prune\, n. [F. prune, from L. prunum a plum. See Plum.]
   A plum; esp., a dried plum, used in cookery; as, French or
   Turkish prunes; California prunes.
   [1913 Webster]

   German prune (Bot.), a large dark purple plum, of oval
      shape, often one-sided. It is much used for preserving,
      either dried or in sirup.

   Prune tree. (Bot.)
   (a) A tree of the genus Prunus (Prunus domestica), which
       produces prunes.
   (b) The West Indian tree, Prunus occidentalis.

   South African prune (Bot.), the edible fruit of a
      sapindaceous tree (Pappea Capensis).
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Damson \Dam"son\ (d[a^]m"z'n), n. [OE. damasin the Damascus
   plum, fr. L. Damascenus. See Damascene.]
   A small oval plum of a blue color, the fruit of a variety of
   the Prunus domestica; -- called also damask plum.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Prunus domestica
    n 1: any of various widely distributed plums grown in the cooler
         temperate areas [syn: common plum, Prunus domestica]