large person vs someone

large person and someone both are nouns.

Word	Noun	Adjective	Verb	Adverb
large person	Yes	No	No	No
someone	Yes	No	No	No

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

large person: a person of greater than average size
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

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

large person (noun)	someone (noun)
a person of greater than average size	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential