Jack is varlet (5)
I believe the answer is:
knave
I believe this is a double definition.
'jack' is the first definition.
(knave can mean a jack playing card)
'is varlet' is the second definition.
(I've seen this in another clue)
(Other definitions for knave that I've seen before include "Villain - jack" , "pack member?" , "[COURT CARD] , maybe" , "Rascal; picture card" , "Unscrupulous fellow" .)