redhead vs someone

redhead and someone both are nouns.

Word	Noun	Adjective	Verb	Adverb
redhead	Yes	No	No	No
someone	Yes	No	No	No

As nouns, someone is a hypernym of redhead; that is, someone is a word with a broader meaning than redhead:

redhead: someone who has red hair
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of redhead include individual, mortal, person, somebody, soul.

redhead (noun)	someone (noun)
black-and-white North American woodpecker having a red head and neck	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential
North American diving duck with a grey-and-black body and reddish-brown head
someone who has red hair