Chap has nothing as complaint (4)
I believe the answer is:
moan
'complaint' is the definition.
(a moan is a complaint or objection)
'chap has nothing' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'has' is an insertion indicator.
'nothing' becomes 'O' (looks like zero - 0).
'man' enclosing 'o' is 'MOAN'.
'as' acts as a link.
(Other definitions for moan that I've seen before include "Murmur of pain; grumble" , "bellyache" , "Complain; rhymes with money lent" , "Low sound of pain" , "Complain mournfully" .)