Do a grinding job (4)
I believe the answer is:
mill
This might be a double definition.
'do' is the first definition.
The definition and answer can be both to do with motion as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
'a grinding job' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I don't see?
Can you help me to learn more?
(Other definitions for mill that I've seen before include "(Pepper) grinder" , "Fist fight" , "Advocate of the utilitarian" , "J.S. - - , philosopher" , "Grind (flour)" .)