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]