Source : Webster's Revised Unabridged Dictionary (1913)

Protasis \Prot"a*sis\, n. [L., fr. Gr. ?, fr. ? to stretch
   before, forward; ? before + ? to stretch.]
   1. A proposition; a maxim. --Johnson.

   2. (Gram.) The introductory or subordinate member of a
      sentence, generally of a conditional sentence; -- opposed
      to {apodosis}. See {Apodosis}.

   3. The first part of a drama, of a poem, or the like; the
      introduction; opposed to {epitasis}. --B. Jonson.