Wanton son visiting Cornish town (5)
I believe the answer is:
loose
'wanton' is the definition.
(synonyms)
'son visiting cornish town' is the wordplay.
'son' becomes 's'.
'visiting' is an insertion indicator.
'cornish town' becomes 'looe' (I've seen this before).
's' inserted within 'looe' is 'LOOSE'.
(Other definitions for loose that I've seen before include "Unfettered" , "Free or immoral" , "Unleash" , "Unattached" , "Showing fast behaviour" .)