I rise in the end and leave (3)
I believe the answer is:
ego
'i' is the definition.
(thesaurus)
'rise in the end and leave' is the wordplay.
'in the end' suggests the final letters.
'and' is a charade indicator (letters next to each other).
'leave' becomes 'go'.
The last letter of 'rise' is 'e'.
'e'+'go'='EGO'
(Other definitions for ego that I've seen before include "Self-esteem, conceit" , "Consciousness" , "(Self-assertive) personality" , "One's sense of self-importance" , "Inflated pride" .)