blood brother vs brother

blood brother and brother both are nouns.

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

As nouns, blood brother and brother are synonyms defined as:

blood brother (noun)	brother (noun)
a male with the same parents as someone else	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	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