man jack vs someone

man jack and someone both are nouns.

Word	Noun	Adjective	Verb	Adverb
man jack	Yes	No	No	No
someone	Yes	No	No	No

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

man jack: a single individual
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of man jack include individual, mortal, person, somebody, soul.

man jack (noun)	someone (noun)
a single individual	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential