ally vs blood brother

ally and blood brother both are nouns.

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

As nouns, blood brother is a hyponym of ally; that is, blood brother is a word with a more specific, narrower meaning than ally:

ally: an associate who provides cooperation or assistance
blood brother: a male sworn (usually by a ceremony involving the mingling of blood) to treat another as his brother

ally (noun)	blood brother (noun)
a friendly nation	a male with the same parents as someone else
an associate who provides cooperation or assistance	a male sworn (usually by a ceremony involving the mingling of blood) to treat another as his brother

ally (verb)	blood brother (verb)
become an ally or associate, as by a treaty or marriage