Orifice (4)
'orifice' is the definition.
(I know that vent is a type of orifice)
This is the entire clue.
(Other definitions for vent that I've seen before include "Orifice" , "Air passage" , "Opening for air/gas" , "Volcanic opening" , "Broadcast" .)
'orifice' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aperture that I've seen before include "Opening, gap" , "Hole, gap" , "Eye" , "Opening, to let light enter a camera perhaps" , "Opening (for a photographer?)" .)