sinus

noun ! Definition from WordNet 3.1, Princeton University. Pronunciation from Wiktionary, via Kaikki.org. More about sinus at Wordnik → Where our words come from →

1. An abnormal passage leading from a suppurating cavity to the body surface.
2. Any of various air-filled cavities especially in the bones of the skull.
3. A wide channel containing blood; does not have the coating of an ordinary blood vessel.