For instance, love of oneself (3)
I believe the answer is:
ego
'oneself' is the definition.
(I've seen this in another clue)
'for instance love' is the wordplay.
'for instance' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'love' becomes 'o' (love means zero in tennis).
'eg'+'o'='EGO'
'of' acts as a link.
(Other definitions for ego that I've seen before include "Self-esteem, sense of self" , "Self-confidence" , "Morale" , "(Person's) sense of self-esteem" , "In Virgil I" .)