small person vs someone

small person and someone both are nouns.

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

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

small person: a person of below average size
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

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

small person (noun)	someone (noun)
a person of below average size	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential