Swindle day after coin value reduced (12)
I believe the answer is:
concentrated
'reduced' is the definition.
('concentrate' can be a synonym of 'reduce')
'swindle day after coin value' is the wordplay.
I cannot really understand how this works, but
'swindle' could be 'con' (synonyms) and 'con' is located in the answer.
'day' could be 'd' (abbreviation for day) and 'd' is located in the answer.
'coin' could be 'cent' (cent is a kind of coin) and 'cent' is present in the answer.
'value' could be 'rate' (both can mean to esteem) and 'rate' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for concentrated that I've seen is " Focused - made denser".)