Reuse (7)
I believe the answer is:
recycle
'reuse' is the definition.
(I know that reuse can be written as recycle)
This is the entire clue.
(Other definitions for recycle that I've seen before include "Use (rubbish) again" , "Behave greenly" , "attempt to save the world?" , "be green" , "What Greens do" .)