monk vs Brother

monk and Brother both are nouns.

Word	Noun	Adjective	Verb	Adverb
monk	Yes	No	No	No
Brother	Yes	No	No	No

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

monk: a male religious living in a cloister and devoting himself to contemplation and prayer and work
Brother: (Roman Catholic Church) a title given to a monk and used as form of address

Other hyponyms of monk include Carthusian, Cistercian, Trappist.

monk (noun)	Brother (noun)
a male religious living in a cloister and devoting himself to contemplation and prayer and work	(Roman Catholic Church) a title given to a monk and used as form of address