Rotating air inlet (3)
I believe the answer is:
ria
'inlet' is the definition.
(I've seen this before)
'rotating air' is the wordplay.
'rotating' says the letters should be written in reverse.
'air' back-to-front is 'RIA'.
(Other definitions for ria that I've seen before include "Coastal inlet" , "inlet between hills" , "Long narrow inlet" , "Irish academy for sciences and humanities, in short" , "Submerged valley" .)