Relaxed solo played with echo (5)
I believe the answer is:
loose
'relaxed' is the definition.
(loose can mean flexible or unrestricted)
'solo played with echo' is the wordplay.
'played with' indicates an anagram (I've seen this in other clues).
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'solo' is an anagram of 'loos'.
'loos'+'e'='LOOSE'
(Other definitions for loose that I've seen before include "Slack or immoral" , "Unfixed" , "Liberal" , "Showing fast behaviour" , "Not firmly fixed" .)