venous sinus vs sinus

venous sinus and sinus both are nouns.

Word	Noun	Adjective	Verb	Adverb
venous sinus	Yes	No	No	No
sinus	Yes	No	No	No

As nouns, venous sinus and sinus are synonyms defined as:

venous sinus and sinus: a wide channel containing blood; does not have the coating of an ordinary blood vessel

venous sinus (noun)	sinus (noun)
a wide channel containing blood; does not have the coating of an ordinary blood vessel	a wide channel containing blood; does not have the coating of an ordinary blood vessel
	any of various air-filled cavities especially in the bones of the skull
	an abnormal passage leading from a suppurating cavity to the body surface