Barrage balloon (5)
I believe the answer is:
blimp
'barrage balloon' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for blimp that I've seen before include "Airship - barrage balloon" , "Small barrage balloon" , "returns one pound to provost" , "Elderly pompous reactionary person" , "aircraft" .)