Lied shiftily about being slack? (4)
I believe the answer is:
idle
'being slack?' is the definition.
(thesaurus)
'lied shiftily' is the wordplay.
'shiftily' is an anagram indicator (I've seen this in other clues).
'lied' anagrammed gives 'IDLE'.
'about' is the link.
(Other definitions for idle that I've seen before include "Do very little" , "'Lazy, not doing anything (4)'" , "Monty Python's Eric, b. 1943" , "Loaf" , "Lazy - vain" .)