Varnish Jack's applied to a pot (5)
I believe the answer is:
japan
'varnish' is the definition.
(thesaurus)
'jack's applied to a pot' is the wordplay.
'jack' becomes 'J' (playing card abbreviation).
'applied to' means one lot of letters go next to another.
'pot' becomes 'pan' (I've seen this in other clues).
'j'+'a'+'pan'='JAPAN'
(Other definitions for japan that I've seen before include "Nippon" , "Land of the Rising Sun" , "East Asian country" , "Twelve [VARNISH]" , "'Country of more than 3,000 islands (5)'" .)