walk-up apartment vs walk-up

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

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

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

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

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

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