Just quits (4)
I believe the answer is:
even
I believe this is a double definition.
'just' is the first definition.
(thesaurus)
'quits' is the second definition.
(as in 'call it quits')
(Other definitions for even that I've seen before include "Pantomime" , "Yet; smooth" , "Flat, regular" , "Like 2,4,6, ..." , "Flat, level" .)