what is sinus for
In anatomy, a sinus is a cavity within a bone or other tissue. Most are commonly found in the bones of the face and connecting with the nasal cavities: 1  Sinus (anatomy) , description of the general term. 2  Paranasal sinuses, air cavities in the cranial bones, especially those near the nose, including: Sinus (anatomy) , description of the general term. 2  Paranasal sinuses, air cavities in the cranial bones, especially those near the nose, including: 3  the maxillary sinuses, also called the maxillary antra and the largest of the paranasal sinuses, are under the eyes, in the maxillary bones.