late 12c., "sufferings of Christ on the Cross," from Old French passion "Christ's passion, physical suffering" (10c.), from Late Latin passionem (nominative passio) "suffering, enduring," from past participle stem of Latin pati "to suffer, endure," possibly from PIE root *pe(i)- "to hurt" (cf. Sanskrit pijati "reviles, scorns," Greek pema "suffering, misery, woe," Old English feond "enemy, devil," Gothic faian "to blame").
Sense extended to sufferings of martyrs, and suffering generally, by early 13c.; meaning "strong emotion, desire" is attested from late 14c., from Late Latin use of passio to render Greek pathos. Replaced Old English þolung (used in glosses to render Latin passio), literally "suffering," from þolian (v.) "to endure."
Sense of "sexual love" first attested 1580s; that of "strong liking, enthusiasm, predilection" is from 1630s. The passion-flower so called from 1630s.