Heard bitter trouble (3)
I believe the answer is:
ail
'trouble' is the definition.
(synonyms)
'heard bitter' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'bitter' becomes 'ale' (type of beer or bitter).
'ale' is a homophone of 'AIL'.
(Other definitions for ail that I've seen before include "Be the worse for wear" , "Afflict; suffer" , "Become unwell" , "Be unwell, suffer" , "Cause to feel indisposed" .)