blind alley vs impasse

blind alley and impasse both are nouns.

Word	Noun	Adjective	Verb	Adverb
blind alley	Yes	No	No	No
impasse	Yes	No	No	No

As nouns, blind alley and impasse are synonyms defined as:

Other synonyms of blind alley include cul de sac, dead-end street.

blind alley (noun)	impasse (noun)
(figurative) a course of action that is unproductive and offers no hope of improvement	a street with only one way in or out
a street with only one way in or out	a situation in which no progress can be made or no advancement is possible