A devastating thing to do (6)
I believe the answer is:
ravage
'do' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how one could define the other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for ravage that I've seen before include "Cause extensive destruction" , "Act like a 6" , "Greatly damage, destroy" , "Lay waste, plunder" , "Wreak havoc upon" .)