Vent or aperture (7)
I believe the answer is:
orifice
I believe this clue is a double definition.
'vent' is the first definition.
(I've seen this before)
'aperture' is the second definition.
(I've seen this before)
(Other definitions for orifice that I've seen before include "Vent" , "Hole in the head, perhaps?" , "Hole, opening" , "provided by gold and diamonds" , "For CIE, I look for an opening" .)