Regret accepting penny with English currency (5)
I believe the answer is:
rupee
'currency' is the definition.
(eg currency of India)
'regret accepting penny with english' is the wordplay.
'regret' becomes 'rue' (to rue something is to regret it).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'penny' becomes 'p' (short for pence).
'with' says to put letters next to each other.
'english' becomes 'E' (abbreviation as in OED).
'rue' going around 'p' is 'rupe'.
'rupe'+'e'='RUPEE'
(Other definitions for rupee that I've seen before include "available without capital holds up" , "Indian coin" , "low cost in Pakistan?" , "Currency of India, Pakistan and Bhutan" , "Indian currency unit" .)