Religious
Middle English: from Old French, from Latin religiosus, from religio ‘reverence, obligation’ (see religion).
wiktionary
From Middle English religiouse, religious, religius, religeous, from Anglo-Norman religieus, religius, from Old French religious, religieux, and their source, Latin religiōsus(“religious, superstitious, conscientious”), from religiō.
etymonline
religious (adj.)
c. 1200, "devout, pious, imbued with or expressive of religious devotion," used of Christians, Jews, pagans; also "belonging to a religious order," from Anglo-French religius, Old French religious (12c., Modern French religieux) and directly from Latin religiosus, "pious, devout, reverencing or fearing the gods," also "religiously careful, anxious, or scrupulous," from religio "religious observance; holiness" (see religion).
The meaning "pertaining to religion" is from 1530s. The transferred sense of "scrupulous, exact, conscientious" is recorded from 1590s but restores or revives a sense right at home among the superstitious Romans. As a noun, from c. 1200 as "persons bound by vow to a religious order;" from late 14c. as "pious persons, the devout." Related: Religiousness.
