Source : Webster's Revised Unabridged Dictionary (1913)

Pitahaya \Pit`a*ha"ya\, n. [Sp., prob. from the native name.]
   (Bot.)
   A cactaceous shrub ({Cereus Pitajaya}) of tropical America,
   which yields a delicious fruit.

Source : WordNet®

pitahaya
     n 1: cactus of the southwestern United States and northern Mexico
          having edible juicy fruit [syn: {pitahaya cactus}, {Acanthocereus
          tetragonus}, {Acanthocereus pentagonus}]
     2: highly colored edible fruit of pitahaya cactus having bright
        red juice; often as large as a peach