Logic. the subject or the predicate of the conclusion of a syllogism; either of two terms that are separated in the premises and brought together in the conclusion.
15.
Archaic. the utmost point, or extremity, of something.
mid-15c., from L. extremus "outermost, utmost," superlative of exterus (see exterior). In English as in Latin, not always felt as a superlative, hence more extreme, most extreme (which were condemned by Johnson). The noun is first recorded 1540s, originally of the end of
life, cf. Latin in extremis. Extreme unction preserves the sense of last, latest (15c.). As a noun, c.1600, in in the extreme, etc. Extremes opposite ends of anything is from 1550s.