Defective firecracker (3)
I believe the answer is:
dud
'defective firecracker' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dud that I've seen before include "Fake -- failure" , "Failure; washout" , "A palindromic washout" , "One failing to work, explode" , "Defective" .)