cul de sac vs dead-end street

cul de sac and dead-end street both are nouns.

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

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

Other synonyms of cul de sac include blind alley, impasse.

cul de sac (noun)	dead-end street (noun)
a street with only one way in or out	a street with only one way in or out
a passage with access only at one end