walk-up vs walk-up apartment

walk-up and walk-up apartment both are nouns.

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

As nouns, walk-up and walk-up apartment are synonyms defined as:

walk-up and walk-up apartment: an apartment in a building without an elevator

walk-up (noun)	walk-up apartment (noun)
an apartment building without an elevator	an apartment in a building without an elevator
an apartment in a building without an elevator

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