half brother vs blood brother

half brother and blood brother both are nouns.

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

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

Other hypernyms of half brother include brother.

half brother (noun)	blood brother (noun)
a brother who has only one parent in common with you	a male with the same parents as someone else
	a male sworn (usually by a ceremony involving the mingling of blood) to treat another as his brother