Poor duke regularly does turn for money (4)
I believe the answer is:
euro
'money' is the definition.
(euro is a currency)
'poor duke regularly does turn' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'does turn' says the letters should be written in reverse.
'poor'+'duke'='poorduke'
The alternate letters of 'poorduke' are 'orue'.
'orue' in reverse letter order is 'EURO'.
'for' is the link.
(Other definitions for euro that I've seen before include "The new international money unit" , "Major currency" , "Currency of France" , "France's unit of currency" , "EU money" .)