The Collaborative International Dictionary of English v.0.48:

Prunus \Pru"nus\, n. [L., a plum tree.] (Bot.)
   A genus of trees with perigynous rosaceous flowers, and a
   single two-ovuled carpel which usually becomes a drupe in
   ripening.
   [1913 Webster]

   Note: Originally, this genus was limited to the plums, then,
         by Linn[ae]us, was made to include the cherries and the
         apricot. Later botanists separated these into several
         genera, as Prunus, Cerasus, and Armeniaca, but
         now, by Bentham and Hooker, the plums, cherries, cherry
         laurels, peach, almond, and nectarine are all placed in
         Prunus.
         [1913 Webster] Prurience

WordNet (r) 3.0 (2006):

Prunus
    n 1: a genus of shrubs and trees of the family Rosaceae that is
         widely distributed in temperate regions [syn: Prunus,
         genus Prunus]