propositus vs someone

propositus and someone both are nouns.

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

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

propositus: the person immediately affected by or concerned with an action
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

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

propositus (noun)	someone (noun)
the person immediately affected by or concerned with an action	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential