brethren vs sect

brethren and sect both are nouns.

Word	Noun	Adjective	Verb	Adverb
brethren	Yes	No	No	No
sect	Yes	No	No	No

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

Other hypernyms of brethren include religious order, religious sect.

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