Psyche part (3)
I believe the answer is:
ego
'psyche part' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ego that I've seen before include "Sense of identity" , "Self-esteem or self-importance" , "(Self-assertive) personality" , "Part of the mind" , "One's self image" .)