early 15c., from O.Fr. transgression (12c.), from L.L. transgressionem (nom. transgressio) "a transgression of the law," from L. "a going over," from transgressus, pp. of transgredi "go beyond," from trans- "across" + gradi (pp. gressus) "to walk, go" (see grade). The verb transgress is recorded from 1520s. Related: Transgressor (late 14c.).