Fails to contain trouble (3)
I believe the answer is:
ail
'trouble' is the definition.
(I know that trouble can be written as ail)
'fails to contain' is the wordplay.
'to contain' indicates a hidden word (words from the clue contain the answer).
'AIL' is hidden in the letters of 'fails'.
(Other definitions for ail that I've seen before include "Be ill or unwell" , "Be unwell, suffer" , "Trouble, afflict; be sickly" , "Sicken" , "Sink" .)