brother vs brotherly

brother is a noun but brotherly is not a noun.

Word	Noun	Adjective	Verb	Adverb
brother	Yes	No	No	No
brotherly	No	Yes	No	Yes

brother (noun)	brotherly (noun)
a male with the same parents as someone else
a male person who is a fellow member (of a fraternity or religion or other group)
a close friend who accompanies his buddies in their activities
used as a term of address for those male persons engaged in the same movement

brother (adjective)	brotherly (adjective)
	like or characteristic of or befitting a brother

brother (adverb)	brotherly (adverb)
	(archaic as adverb) in a manner characteristic of a brother