Concept working after turning it on (6)
I believe the answer is:
notion
'concept' is the definition.
(notion is a kind of concept)
'working after turning it on' is the wordplay.
'working' becomes 'on' (**).
'after' is a charade indicator (letters next to each other).
'turning' shows that the letters should be reversed in order.
'it'+'on'='iton'
'iton' in reverse letter order is 'noti'.
'on' put after 'noti' is 'NOTION'.
(Other definitions for notion that I've seen before include "A vague and possibly incorrect opinion" , "clue" , "desire" , "Whimsical idea or small sewing article" , "Concept, belief" .)