Expiate (5)
I believe the answer is:
atone
'expiate' is the definition.
(I know that expiate can be written as atone)
This is the entire clue.
(Other definitions for atone that I've seen before include "Make up, compensate (for)" , "Make amends, being at one" , "remedy" , "Make redress" , "Make amends (for something)" .)