mixed-blood vs somebody

mixed-blood and somebody both are nouns.

Word	Noun	Adjective	Verb	Adverb
mixed-blood	Yes	No	No	No
somebody	Yes	No	No	No

As nouns, somebody is a hypernym of mixed-blood; that is, somebody is a word with a broader meaning than mixed-blood:

mixed-blood: a person whose ancestors belonged to two or more racial groups
somebody: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of mixed-blood include individual, mortal, person, someone, soul.

mixed-blood (noun)	somebody (noun)
a person whose ancestors belonged to two or more racial groups	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential