One's never even right in head after left in agony (10)
I believe the answer is:
palindrome
'one's never even' is the definition.
I can't tell whether this definition defines the answer.
'right in head after left in agony' is the wordplay.
'right in head' becomes 'drome' (I can't explain this - if you can you should believe this answer much more).
'after' says to put letters next to each other.
'left' becomes 'L' (common abbreviation).
'in' indicates putting letters inside.
'agony' becomes 'pain' (I've seen this before).
'l' put into 'pain' is 'palin'.
'drome' after 'palin' is 'PALINDROME'.
Can you help me to learn more?
(Other definitions for palindrome that I've seen before include "Word(s) reading the same forward and back" , "Bob, perhaps" , "Word reading same forwards and back" , "Mum, say" , "Mum, perhaps" .)