righthander vs someone

righthander and someone both are nouns.

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

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

righthander: a person who uses the right hand more skillfully than the left
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

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

righthander (noun)	someone (noun)
a person who uses the right hand more skillfully than the left	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential