ethmoidal sinus vs sinus

ethmoidal sinus and sinus both are nouns.

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

As nouns, sinus is a hypernym of ethmoidal sinus; that is, sinus is a word with a broader meaning than ethmoidal sinus:

ethmoidal sinus: a sinus of the meatuses of the nasal cavity (behind the bridge of the nose)
sinus: any of various air-filled cavities especially in the bones of the skull

ethmoidal sinus (noun)	sinus (noun)
a sinus of the meatuses of the nasal cavity (behind the bridge of the nose)	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