Regretted sounding coarse (4)
I believe the answer is:
rued
'regretted' is the definition.
('rue' can be a synonym of 'regret')
'sounding coarse' is the wordplay.
'sounding' indicates a 'sounds like' (homophone) clue.
'coarse' becomes 'rude' (I've seen this before).
'rude' is a homophone of 'RUED'.
(Other definitions for rued that I've seen before include "Bitterly regretted" , "Was sorry" , "Was contrite about" , "was remorseful" , "'Regretted, repented (4)'" .)