cul de sac vs dead end

cul de sac and dead end both are nouns.

Word	Noun	Adjective	Verb	Adverb
cul de sac	Yes	No	No	No
dead end	Yes	No	No	No

As nouns, cul de sac and dead end are synonyms defined as:

Other synonyms of cul de sac include cul.

cul de sac (noun)	dead end (noun)
a street with only one way in or out	a passage with access only at one end
a passage with access only at one end	a situation in which no progress can be made or no advancement is possible