In retrospect, some regret tantalising gossip (6)
I believe the answer is:
natter
'gossip' is the definition.
(synonyms)
'in retrospect some regret tantalising' is the wordplay.
'in retrospect' shows that the letters should be reversed in order.
'some' indicates a hidden word (some of the parts of the word are used).
'rettan' can be found hidden inside 'regret tantalising'.
'rettan' reversed gives 'NATTER'.
(Other definitions for natter that I've seen before include "Talk socially without exchanging too much information" , "idle talk" , "Gossip, maybe annoyingly" , "Chat casually" , "Chat - gossip" .)