half brother vs brother

half brother and brother both are nouns.

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

As nouns, brother is a hypernym of half brother; that is, brother is a word with a broader meaning than half brother:

Other hypernyms of half brother include blood brother.

half brother (noun)	brother (noun)
a brother who has only one parent in common with you	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