buddy vs brother

buddy and brother both are nouns.

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

As nouns, buddy and brother are synonyms defined as:

buddy and brother: a close friend who accompanies his buddies in their activities

Other synonyms of buddy include chum, crony, pal, sidekick.

buddy (noun)	brother (noun)
a close friend who accompanies his buddies in their activities	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