paranasal sinus

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy A number of air-filled spaces, or sinuses, within the bones of the skull and face.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of the paired sinuses in the bones of the face adjacent to the nasal cavity that are lined with mucous membrane that is continuous with the lining of the nasal cavities