n. pl. prot·a·ses (-sēz′)
1. Grammar The dependent clause of a conditional sentence, as if it rains in The game will be canceled if it rains.
2. The first part of an ancient Greek or Roman drama, in which the characters and subject are introduced.

[Late Latin, proposition, first part of a play, from Greek, premise of a syllogism, conditional clause, from proteinein, prota-, to propose : pro-, forward; see pro-2 + teinein, to stretch; see ten- in Indo-European roots.]

pro·tat′ic (prŏ-tăt′ĭk, prō-) adj.