Criminal got off after sanction (7)
I believe the answer is:
consent
'sanction' is the definition.
(thesaurus)
'criminal got off after' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'got off' becomes 'sent' ('send' can be a synonym of 'get off').
'after' means one lot of letters go next to another.
'con'+'sent'='CONSENT'
(Other definitions for consent that I've seen before include "Agree or permit" , "Give approval" , "Agree(ment)" , "authorisation" , "Say yes to something" .)