Relaxed sons in Cornish town (5)
I believe the answer is:
loose
'relaxed' is the definition.
(loose can mean flexible or unrestricted)
'sons in cornish town' is the wordplay.
'sons' becomes 's'.
'in' indicates putting letters inside.
'cornish town' becomes 'looe' (I've seen this in other clues).
's' going inside 'looe' is 'LOOSE'.
(Other definitions for loose that I've seen before include "Relaxed; set free" , "Not restrained or attached" , "Unconfined" , "Not bound" , "Imprecise" .)