Self-absorbed person (9)
(Other definitions for egomaniac that I've seen before include "Obsessively self-centred person" , "Excessively self-absorbed person" , "he thinks "it's all about ME"" , "Abnormally egotistical person" , "One who's self-obsessed" .)
'self-absorbed person' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for egotist that I've seen before include "One who is concerned only with self" , "Self-interested person" , "What I want" , "Boastful person" , "Conceited and self-centred person" .)