Regret being less than true (3)
I believe the answer is:
rue
'regret' is the definition.
(to rue something is to regret it)
'less than true' is the wordplay.
'RUE' is hidden in amongst the letters.
However, I'm uncertain how this is indicated.
'being' is the link.
Can you help me to learn more?
(Other definitions for rue that I've seen before include "Regret in a French street" , "Regret; road (Fr.)" , "Wish not to have been" , "At one time, pity" , "Regret or repent" .)