Regrets using trick for the audience (4)
I believe the answer is:
rues
'regrets' is the definition.
('rue' can be a synonym of 'regret')
'trick for the audience' is the wordplay.
'trick' becomes 'ruse' (I've seen this before).
'for the audience' shows a homophone (sound like) (how an audience might hear it).
'ruse' is a homophone of 'RUES'.
'using' is the link.
(Other definitions for rues that I've seen before include "Is sorry for - plants" , "Regrets, to be sure" , "Bemoans" .)