monastic vs Brother

monastic and Brother both are nouns.

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

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

monastic: 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 monastic include Carthusian, Cistercian, Trappist.

monastic (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

monastic (adjective)	Brother (adjective)
of communal life sequestered from the world under religious vows