Regrets the disheartening loss of rupees (4)
I believe the answer is:
rues
'loss of rupees' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.
'regrets the disheartening' is the wordplay.
'regrets' becomes 'ruefulnesses' ('ruefulness' can be a synonym of 'regret').
'the disheartening' suggests removing the centre.
'ruefulnesses' with its middle taken out is 'RUES'.
Can you help me to learn more?
(Other definitions for rues that I've seen before include "Is sorry for - plants" , "Regrets, to be sure" , "Bemoans" .)