brethren vs religious order

brethren and religious order both are nouns.

Word	Noun	Adjective	Verb	Adverb
brethren	Yes	No	No	No
religious order	Yes	No	No	No

As nouns, religious order is a hypernym of brethren; that is, religious order is a word with a broader meaning than brethren:

Other hypernyms of brethren include religious sect, sect.

brethren (noun)	religious order (noun)
(plural) the lay members of a male religious order	a subdivision of a larger religious group