walk-up vs apartment

walk-up and apartment both are nouns.

Word	Noun	Adjective	Verb	Adverb
walk-up	Yes	Yes	No	No
apartment	Yes	No	No	No

As nouns, apartment is a hypernym of walk-up; that is, apartment is a word with a broader meaning than walk-up:

Other hypernyms of walk-up include flat.

walk-up (noun)	apartment (noun)
an apartment building without an elevator	a suite of rooms usually on one floor of an apartment house
an apartment in a building without an elevator

walk-up (adjective)	apartment (adjective)
a building with no elevator