Cavity in the bones of the skull (5)
I believe the answer is:
sinus
(Other definitions for sinus that I've seen before include "Bodily cavity" , "Hole in the head" , "Nasal cavity" , "Head space" , "Cavity within a bone" .)
I believe the answer is:
sinus
(Other definitions for sinus that I've seen before include "Bodily cavity" , "Hole in the head" , "Nasal cavity" , "Head space" , "Cavity within a bone" .)