Type of headache (5)
I believe the answer is:
sinus
'type of headache' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sinus that I've seen before include "Cavity in the facial bones" , "Nasal cavity" , "Air-filled cavity in one's head" , "Passage in the head" , "Cavity linked to nose" .)