Many trees of back rest (6)
I believe the answer is:
forest
'many trees of back rest' is the definition.
I can't judge whether this defines the answer.
'of back rest' is the wordplay.
'back' says the letters should be written backwards.
'of' written backwards gives 'fo'.
'fo'+'rest'='FOREST'
Can you help me to learn more?
(Other definitions for forest that I've seen before include "Sherwood or Pine, say" , "Thick growth of trees" , "green area" , "Grow more rigid" , "Large, densely-wooded area" .)