(anatomy, zootomy) A pouch or cavity in a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities (the paranasal sinus).

(anatomy) Any of a number of air-filled spaces, or sinuses, within the bones of the skull and face.

(anatomy) A paranasal sinus found in the body of the maxilla.

(anatomy) A paranasal sinus situated behind the superciliary arches.

(anatomy) A paranasal sinus contained within the body of the sphenoid bone.

(anatomy) Any of several paranasal sinuses enclosed within the ethmoid bone.

Alternative form of sphenoid sinus

(anatomy) A large collection of veins in the heart wall that collects blood from the myocardium and empties into the right atrium.

(medicine, colloquial) Sinus tachycardia.

(medicine, colloquial) Sinus bradycardia.