Boaster? Eccentric? Come again? (9)
I believe the answer is:
egomaniac
'boaster?' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'eccentric? come again?' is the wordplay.
'eccentric?' indicates an anagram (I've seen 'eccentric' mean this).
'come'+'again'='comeagain'
'comeagain' with letters rearranged gives 'EGOMANIAC'.
Can you help me to learn more?
(Other definitions for egomaniac that I've seen before include "Self-obsessed person" , "Come again (anag.)" , "Excessively self-absorbed person" , "One who's self-obsessed" , "self-obsessed individual" .)