mixed-blood vs octoroon

mixed-blood and octoroon both are nouns.

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

As nouns, octoroon is a hyponym of mixed-blood; that is, octoroon is a word with a more specific, narrower meaning than mixed-blood:

mixed-blood: a person whose ancestors belonged to two or more racial groups
octoroon: an offspring of a quadroon and a white parent; a person who is one-eighth black

Other hyponyms of mixed-blood include mulatto, quadroon, half-caste, Metis.

mixed-blood (noun)	octoroon (noun)
a person whose ancestors belonged to two or more racial groups	an offspring of a quadroon and a white parent; a person who is one-eighth black