religious vs friar

religious and friar both are nouns.

Word	Noun	Adjective	Verb	Adverb
religious	Yes	Yes	No	No
friar	Yes	No	No	No

As nouns, friar is a hyponym of religious; that is, friar is a word with a more specific, narrower meaning than religious:

religious: a member of a religious order who is bound by vows of poverty and chastity and obedience
friar: a male member of a religious order that originally relied solely on alms

Other hyponyms of religious include mendicant, monastic, monk, Benedictine, Jesuit, nun, eremite, cenobite, coenobite, superior, votary.

religious (noun)	friar (noun)
a member of a religious order who is bound by vows of poverty and chastity and obedience	a male member of a religious order that originally relied solely on alms

religious (adjective)	friar (adjective)
having or showing belief in and reverence for a deity
of or relating to clergy bound by monastic vows
concerned with sacred matters or religion or the church
extremely scrupulous and conscientious