What's the "een" in Halloween?
c.1200, "devout, pious, imbued with or expressive of religious devotion," from Anglo-French religius, Old French religious (12c., Modern French religieux) and directly from Latin religiosus, from religio (see religion). Meaning "pertaining to religion" is from 1530s. Transferred sense of "scrupulous, exact" is recorded from 1590s. Related: Religiousness.