Suffer in terrible trouble (3)
I believe the answer is:
let
'suffer' is the definition.
(thesaurus)
'in terrible trouble' is the wordplay.
'in' indicates a hidden word.
'LET' is hidden within 'terrible trouble'.
(Other definitions for let that I've seen before include "Allow; rental period" , "Allow; tennis fault" , "Rent out: grant" , "Service that must be repeated" , "Won't stop you" .)