Posted a second time, intended to be heard, leading to bitterness (10)
I believe the answer is:
resentment
'to bitterness' is the definition.
(synonyms)
'posted a second time intended to be heard leading' is the wordplay.
'posted a second time' becomes 'resent' (sent again).
'intended' becomes 'meant' (to mean something is to intend it).
'to be heard' indicates a 'sounds like' (homophone) clue.
'leading' is a charade indicator (letters next to each other).
'meant' is a homophone of 'ment'.
'resent'+'ment'='RESENTMENT'
(Other definitions for resentment that I've seen before include "Hard feelings" , "ill-feeling" , "offence" , "Annoyance" , "Ill will" .)