Varnish judge used on a vessel (5)
I believe the answer is:
japan
'varnish' is the definition.
(thesaurus)
'judge used on a vessel' is the wordplay.
'judge' becomes 'j' (abbreviation for judge).
'used on' means one lot of letters go next to another.
'vessel' becomes 'pan' (I have seen 'Shallow vessel ' mean 'pan' so perhaps 'vessel' could also mean 'pan').
'j'+'a'+'pan'='JAPAN'
(Other definitions for japan that I've seen before include "Country in East Asia" , "Twelve [VARNISH]" , "'Country of more than 3,000 islands (5)'" , "Nippon" , "East Asian country" .)