1590s, from French irréligion (16c.) or directly from Late Latin irreligionem (nominative irreligio) "irreligion, impiety," from assimiliated form of in- "not" (see in- (1)) + religio (see religion).
irregardless
irregular
irregularity
irrelevance
irrelevant
irreligion
irreligious
irremediable
irremediably
irremovable
irreparable