Jack’s cunning art (3)
I believe the answer is:
tar
'jack's' is the definition.
(thesaurus)
'cunning art' is the wordplay.
'cunning' indicates an anagram.
'art' is an anagram of 'TAR'.
(Other definitions for tar that I've seen before include "Pitch; sailor" , "Kind of rat for sailor" , "Slang sailor or road surfacing material" , "It paves the way" , "Informal sailor or road surfacing material" .)