Nuns stripped on ramble to relax (6)
I believe the answer is:
unwind
'to relax' is the definition.
(synonyms)
'nuns stripped on ramble' is the wordplay.
'stripped' means to look at the middle letters (outside letters removed).
'on' says to put letters next to each other.
'ramble' becomes 'wind' (wind can mean to ramble or meander).
The centre of 'nuns' is 'un'.
'un'+'wind'='UNWIND'
(Other definitions for unwind that I've seen before include "Relax like spring?" , "Straighten out like snake" .)