Its back is said to get rough treatment (8)
I believe the answer is:
envelope
'treatment' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for envelope that I've seen before include "Wrapper for 31ac" , "Postal wrapper" , "Coat" , "Even pole, strangely, can contain a letter" , "Paper wrapper" .)