frontal sinus vs sinus

frontal sinus and sinus both are nouns.

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

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

frontal sinus: one of a pair of cavities in the frontal bone
sinus: any of various air-filled cavities especially in the bones of the skull

frontal sinus (noun)	sinus (noun)
one of a pair of cavities in the frontal bone	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