Source : Webster's Revised Unabridged Dictionary (1913)

Pistachio \Pis*ta"chio\, n.
   1. The small anacardiaceous tree, of southern Europe and Asia
      Minor, which bears the pistachio nut.

   2. (Cookery) The flavor of the pistachio nut, or an ice or
      confection flavored with it.

   3. Pistachio green.

Pistachio \Pis*ta"chio\, n. [It. pistacchio (cf. Sp. pistacho,
   F. pistache), fr. L. pistacium, Gr. ?, ?, fr. Per. pistah.
   Cf. {Fistinut}.] (Bot.)
   The nut of the {Pistacia vera}, a tree of the order
   {Anacardiace[ae]}, containing a kernel of a pale greenish
   color, which has a pleasant taste, resembling that of the
   almond, and yields an oil of agreeable taste and odor; --
   called also {pistachio nut}. It is wholesome and nutritive.
   The tree grows in Arabia, Persia, Syria, and Sicily. [Written
   also {pistachia}.]

Source : WordNet®

pistachio
     n 1: small tree of southern Europe and Asia Minor bearing small
          hard-shelled nuts [syn: {Pistacia vera}, {pistachio tree}]
     2: nut of Mediterranean trees having an edible green kernel
        [syn: {pistachio nut}]