Anger after question on unknown eccentric (6)
I believe the answer is:
quirky
'eccentric' is the definition.
(thesaurus)
'anger after question on unknown' is the wordplay.
'anger' becomes 'irk' (irking is a kind of angering**).
'after' is a charade indicator (letters next to each other).
'question' becomes 'qu'.
'on' is a charade indicator (letters next to each other).
'unknown' becomes 'y' (algebra).
'irk' put after 'qu' is 'quirk'.
'quirk'+'y'='QUIRKY'
(Other definitions for quirky that I've seen before include "Peculiar in behaviour" , "'Kinky, off-beat (6)'" , "Idiosyncratic" .)