The Collaborative International Dictionary of English v.0.48:

Persimmon \Per*sim"mon\, n. [Virginia Indian.] (Bot.)
   An American tree (Diospyros Virginiana) and its fruit,
   found from New York southward. The fruit is like a plum in
   appearance, but is very harsh and astringent until it has
   been exposed to frost, when it becomes palatable and
   nutritious.
   [1913 Webster]

   Japanese persimmon, Diospyros Kaki and its red or yellow
      edible fruit, which outwardly resembles a tomato, but
      contains a few large seeds.
      [1913 Webster]

WordNet (r) 3.0 (2006):

persimmon
    n 1: any of several tropical trees of the genus Diospyros [syn:
         persimmon, persimmon tree]
    2: orange fruit resembling a plum; edible when fully ripe