Religious means connected with faith and God, or deeply believing. Religious belief, a religious family, religious about it.
It does two jobs: describing the subject matter, as in religious education, and describing a person's commitment. Loosely it means scrupulously regular — religious about her exercise — which keeps the sense of devotion without the faith. Note that in Catholic use a religious is a member of an order, used as a noun.
1adjectivereligiousConnected with faith and God.
“Christmas is a religious holiday, but many people celebrate it without going to church.”
2adjectivescrupulouslyScrupulously regular.
“He's religious about his morning run and never misses a day.”
Too few real examples of this word to estimate which sense is commonest.
religious is a quality of faith or devotion.
Latin religiosus comes from religio, reverence or scruple. Its own root is disputed, perhaps meaning to bind fast.
Latin
religiōsus — religious, superstitious, conscientious
Old French
religious
Anglo-Norman
religieus
Middle English
religiouse
English, today
religious
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. a doublet of religieux.
Etymology from Wiktionary, CC BY-SA