Repair rats (4)
I believe the answer is:
darn
'repair' is the definition.
(darning is a kind of repairing)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for darn that I've seen before include "Repair (with needle)" , "Repair (sock)" , "curse" , "Repair with wool" , "Mend (woollens)" .)