I say who's closer (3)
I believe the answer is:
ego
'i' is the definition.
('I' in Latin)
'say who's closer' is the wordplay.
'say' becomes 'eg' (both can mean for example).
'closer' says to take the final letters (the letter which 'closes' the word).
The last letter of 'who' is 'o'.
'eg'+'o'='EGO'
(Other definitions for ego that I've seen before include "In Virgil I" , "Conscious mind" , "Selfishness" , "Part of the mind" , "One's image of oneself" .)