There's no sole way to relax (6)
I believe the answer is:
loosen
'to relax' is the definition.
('loosen' can be a synonym of 'relax')
'there's no sole way' is the wordplay.
'there's' is a charade indicator (letters next to each other).
'way' is an anagram indicator (another way of arranging the letters).
'no'+'sole' is 'nosole'.
'nosole' is an anagram of 'LOOSEN'.
(Other definitions for loosen that I've seen before include "Make less tight, slacken" , "Relax the tension" , "Untie, relax" , "Work free" , "relax or tear apart" .)