late 15c., transgressen, "to sin," from Old French transgresser (14c.), from Latin transgressus, past participle of transgredi "step across, step over; climb over, pass, go beyond," from trans "across, beyond" (see trans-) + gradi (past participle gressus) "to walk, go" (from PIE root *ghredh- "to walk, go") . Related: Transgressed; transgressing.
word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).