Brother vs monastic

Brother and monastic both are nouns.

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

As nouns, monastic is a hypernym of Brother; that is, monastic is a word with a broader meaning than Brother:

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

Other hypernyms of Brother include monk.

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

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