six-footer vs mortal

six-footer and mortal both are nouns.

Word	Noun	Adjective	Verb	Adverb
six-footer	Yes	No	No	No
mortal	Yes	Yes	No	No

As nouns, mortal is a hypernym of six-footer; that is, mortal is a word with a broader meaning than six-footer:

six-footer: a person who is at least six feet tall
mortal: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of six-footer include individual, person, somebody, someone, soul.

six-footer (noun)	mortal (noun)
a person who is at least six feet tall	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

six-footer (adjective)	mortal (adjective)
	subject to death
	unrelenting and deadly
	involving loss of divine grace or spiritual death
	causing or capable of causing death