Fixes high-backed benches (7)
I believe the answer is:
settles
'backed benches' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for settles that I've seen before include "Comes to rest" , "seating" , "Long wooden benches with backs" , "furniture" , "Resolves" .)