The Collaborative International Dictionary of English v.0.48:

Diastase \Di"a*stase\, n. [Gr. ? separation, fr. ?, ? to stand
   apart; dia` through + ?, ?, to stand, set: cf. F. diastase.
   Cf. Diastasis.] (Physiol. Chem.)
   A soluble enzyme, capable of converting starch and dextrin
   into sugar.
   [1913 Webster]

   Note: The name is more particularly applied to that enzyme
         formed during the germination of grain, as in the
         malting of barley; but it is also occasionally used to
         designate the amylolytic enzyme contained in animal
         fluids, as in the saliva.
         [1913 Webster]