Source : Webster's Revised Unabridged Dictionary (1913)

Papain \Pa*pa"in\, n. [From {Papaw}.] (Physiol. Chem.)
   A proteolytic ferment, like trypsin, present in the juice of
   the green fruit of the papaw ({Carica Papaya}) of tropical
   America.

Source : WordNet®

papain
     n : a proteolytic enzyme obtained from the unripe papaya; used
         as a meat tenderizer