sinus
n. countable C1 Advanced US //ˈsaɪnəs// UK //sˈaɪnəs// si·nus
n. a hollow space or pocket inside your body, especially the ones in the bones of your face near your nose.
n. a cavity or hollow space within a bone or other tissue, most commonly referring to the air-filled paranasal cavities in the skull.
My sinuses feel very blocked because of this cold.
Chronic sinus infections can cause significant pressure and pain behind the eyes and cheeks.
The surgeon carefully navigated the narrow passages of the ethmoid sinus to remove the blockage and restore normal drainage for the patient.
Usage
Often used in the plural when referring to the facial cavities.