Disappointed (3,4)
I believe the answer is:
let down
'disappointed' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for let down that I've seen before include "Disappoint or fail - or lengthen garment" , "Failed - deflated" , "Disappoint, fail to support" , "Disappoint, fail to keep promise" , "Aircraft descent" .)