six-footer vs somebody

six-footer and somebody both are nouns.

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

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

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

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

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