Air of invention (4)
I believe the answer is:
vent
'air' is the definition.
(both can mean to express or reveal)
'of invention' is the wordplay.
'of' says the answer is hidden in the clue.
'VENT' can be found hidden inside 'invention'.
(Other definitions for vent that I've seen before include "[BLOWHOLE] ?" , "Give outlet as to feelings" , "Broadcast" , "Express freely as with emotions" , "Opening for air" .)