sinus vs venous sinus

sinus and venous sinus both are nouns.

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

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

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

sinus (noun)	venous 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