Origin: 1175–1225; ME (< OF) < L
religiōsus, equiv. to
religi(
ō)
religion +
-ōsus -ous 
Related forms: re⋅li⋅gious⋅ly, adverb
re⋅li⋅gious⋅ness, noun
Synonyms:
2. reverent. Religious, devout, pious indicate a spirit of reverence toward God. Religious is a general word, applying to whatever pertains to faith or worship: a religious ceremony. Devout indicates a fervent spirit, usually genuine and often independent of outward observances: a deeply devout though unorthodox church member. Pious implies constant attention to, and extreme conformity with, outward observances. It can also suggest sham or hypocrisy: a pious hypocrite. 3. devoted, unswerving, meticulous.
Antonyms:
2. impious.