A curmudgeon finally put in a few coins, showing remorse (7)
I believe the answer is:
penance
'remorse' is the definition.
(I've seen this before)
'a curmudgeon finally put in a few coins' is the wordplay.
'finally' indicates one should take the final letters.
'put in' indicates putting letters inside.
'a few coins' becomes 'pence'.
The final letter of 'curmudgeon' is 'n'.
'a'+'n'='an'
'an' inserted into 'pence' is 'PENANCE'.
'showing' acts as a link.
(Other definitions for penance that I've seen before include "Self-inflicted punishment for wrongdoing" , "Punishment inflicted on oneself" , "Self-imposed punishment" , "Act of atonement" , "Reparation" .)