Knack; deceive (5)
I believe the answer is:
trick
This clue is a double definition.
'knack' is the first definition.
(thesaurus)
'deceive' is the second definition.
(tricking is a kind of deceiving)
(Other definitions for trick that I've seen before include "Mischievous joke" , "Deceive, perhaps with cards" , "Characteristic habit" , "Deception or illusion" , "Sleight of hand" .)