Returning, go off peak (3)
I believe the answer is:
tor
'peak' is the definition.
(a tor is a rocky peak)
'returning go off' is the wordplay.
'returning' shows that the letters should be reversed in order.
'go off' becomes 'rot' (I've seen this before).
'rot' in reverse letter order is 'TOR'.
(Other definitions for tor that I've seen before include "(Dartmoor) rocky hill" , "Rot on a hill in Devon" , "Fermenting agent" , "feature of Glastonbury" , "fell" .)