protasis

[prot-uh-sis] /ˈprɒt ə sɪs/
noun, plural protases
[prot-uh-seez] /ˈprɒt əˌsiz/ (Show IPA)
1.
the clause expressing the condition in a conditional sentence, in English usually beginning with if.
Compare apodosis.
2.
the first part of an ancient drama, in which the characters are introduced and the subject is proposed.
Compare catastasis, catastrophe (def 4), epitasis.
3.
(in Aristotelian logic) a proposition, especially one used as a premise in a syllogism.
Origin
1610-20; < Late Latin: introduction in a drama < Greek prótasis proposition, literally, a stretching forward, equivalent to pro- pro-2 + tásis a stretching (ta-, verbid stem of teínein to stretch + -sis -sis)
British Dictionary definitions for protasis

protasis

/ˈprɒtəsɪs/
noun (pl) -ses (-siːz)
1.
(logic, grammar) the antecedent of a conditional statement, such as it rains in if it rains the game will be cancelled Compare apodosis
2.
(in classical drama) the introductory part of a play
Derived Forms
protatic (prɒˈtætɪk) adjective
Word Origin
C17: via Latin from Greek: a proposal, from pro- before + teinein to extend