Regret discourteous daughter leaving (3)
I believe the answer is:
rue
'regret' is the definition.
(I've seen this before)
'discourteous daughter leaving' is the wordplay.
'discourteous' becomes 'rude' (I've seen this before).
'daughter' becomes 'd'.
'leaving' is a deletion indicator.
'rude' with 'd' removed is 'RUE'.
(Other definitions for rue that I've seen before include "Feel remorse" , "Regret or repent" , "The 'herb of grace'" , "Fish eggs" , "Cry" .)