ethmoid sinus vs ethmoidal sinus

ethmoid sinus and ethmoidal sinus both are nouns.

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

As nouns, ethmoid sinus and ethmoidal sinus are synonyms defined as:

ethmoid sinus and ethmoidal sinus: a sinus of the meatuses of the nasal cavity (behind the bridge of the nose)

Other synonyms of ethmoid sinus include sinus ethmoidales.

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