I had existence and personality (8)
I believe the answer is:
identity
'personality' is the definition.
(I know that identity is a type of personality)
'i had existence' is the wordplay.
'i had' becomes 'i'd' (I'd).
'existence' becomes 'entity' (I've seen this in another clue).
'id'+'entity'='IDENTITY'
'and' acts as a link.
(Other definitions for identity that I've seen before include "It's on the cards" , "Sameness - individuality" , "Individuality providing recognition" , "Individuality or singularity" , "Individual characteristics by which one is recognised" .)