Sin or stray (3)
I believe the answer is:
err
I believe this is a double definition.
'sin' is the first definition.
(to sin is to err morally)
'stray' is the second definition.
(I know that stray can be written as err)
(Other definitions for err that I've seen before include "Boob" , "'to... is human,to forgive divine'" , "Sin" , "Make mistakes" , "Make mistake in Canberra" .)