The Collaborative International Dictionary of English v.0.48:

Protasis \Prot"a*sis\ (pr[o^]t"[.a]*s[i^]s), n. [L., fr. Gr.
   pro`tasis, fr. protei`nein to stretch before, forward; pro`
   before + tei`nein to stretch.]
   1. A proposition; a maxim. --Johnson.
      [1913 Webster]

   2. (Gram.) The introductory or subordinate member of a
      sentence, generally of a conditional sentence; -- opposed
      to apodosis. See Apodosis.
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   3. The first part of a drama, of a poem, or the like; the
      introduction; opposed to epitasis. --B. Jonson.
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