Relax on sole recreation (6)
I believe the answer is:
loosen
'relax' is the definition.
(I know that relax can be written as loosen)
'on sole recreation' is the wordplay.
'recreation' indicates an anagram.
'on'+'sole'='onsole'
'onsole' with letters rearranged gives 'LOOSEN'.
(Other definitions for loosen that I've seen before include "Make less tight, slacken" , "Work free" , "Undo a little" , "Undo, make less tight" , "Untie, relax" .)