DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   sinus
       n 1: an abnormal passage leading from a suppurating cavity to
            the body surface [syn: fistula, sinus]
       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 [syn: venous sinus, sinus]