cul vs cul de sac

cul and cul de sac both are nouns.

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

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

Other synonyms of cul include dead end.

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