Nothing in the New Testament is negative (3)
I believe the answer is:
not
'is negative' is the definition.
(thesaurus)
'nothing in the new testament' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'in the' indicates putting letters inside.
'new testament' becomes 'nt'.
'o' going into 'nt' is 'NOT'.
(Other definitions for not that I've seen before include "Word of denial" , "Word of negation" , "In no way, never" , "Having close-cut hair" , "Negation of what follows" .)