sphenoid

Definition of sphenoid sinus
National Cancer Institute

sphenoid sinus

(SFEE-noyd SY-nus)
A type of paranasal sinus (a hollow space in the bones around the nose). There are two large sphenoid sinuses in the sphenoid bone, which is behind the nose between the eyes. The sphenoid sinuses are lined with cells that make mucus to keep the nose from drying out.

Source: NCI Dictionary of Cancer Terms