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