A mistake in the chit (4)
I believe the answer is:
slip
I believe this clue is a double definition.
'a mistake' is the first definition.
(a slip is a blunder or mistake)
'chit' is the second definition.
(thesaurus)
'in the' acts as a link.
(Other definitions for slip that I've seen before include "Glide; petticoat" , "Error; watered clay" , "He should take his chances" , "Clay, water mix; fielder" , "Careless mistake" .)