"sinus" in the noun sense
1. fistula, sinus
an abnormal passage leading from a suppurating cavity to the body surface
any of various air-filled cavities especially in the bones of the skull
3. venous sinus, sinus
a wide channel containing blood does not have the coating of an ordinary blood vessel
Source: WordNet® (An amazing lexical database of English)
Princeton University "About WordNet®."
WordNet®. Princeton University. 2010.
View WordNet® License