I, for instance, have nothing (3)
I believe the answer is:
ego
'i' is the definition.
(thesaurus)
'for instance have nothing' is the wordplay.
'for instance' becomes 'eg' ('e.g.' can be a synonym of 'for instance').
'have' says to put letters next to each other.
'nothing' becomes 'o' (looks like zero - 0).
'eg'+'o'='EGO'
(Other definitions for ego that I've seen before include "One's sense of self-importance" , "Self-esteem, sense of self" , "number one" , "Self-confidence" , "One's image of oneself" .)