The Collaborative International Dictionary of English v.0.48:

Cashew \Ca*shew"\ (k[.a]*sh[=oo]"), n. [F. acajou, for cajou,
   prob. from Malay k[=a]yu tree; cf. Pg. acaju, cf. Acajou.]
   1. (Bot.) A tree (Anacardium occidentale) of the same
      family which the sumac. It is native in tropical America,
      but is now naturalized in all tropical countries. Its
      fruit, a kidney-shaped nut, grows at the extremity of an
      edible, pear-shaped hypocarp, about three inches long.
      [1913 Webster]

   2. the cashew nut.
      [PJC]

   Cashew nut, the large, kidney-shaped fruit of the cashew,
      which is edible after the caustic oil has been expelled
      from the shell by roasting the nut.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Anacardium occidentale
    n 1: tropical American evergreen tree bearing kidney-shaped nuts
         that are edible only when roasted [syn: cashew, cashew
         tree, Anacardium occidentale]