Turn on European self-esteem (3)
I believe the answer is:
ego
'self-esteem' is the definition.
(I've seen this before)
'turn on european' is the wordplay.
'turn' is a reversal indicator.
'on' becomes 'og' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'european' becomes 'e' (abbreviation e.g. EU).
'og'+'e'='oge'
'oge' in reverse letter order is 'EGO'.
Can you help me to learn more?
(Other definitions for ego that I've seen before include "One's sense of self-importance" , "Self-esteem, conceit" , "One's self-image" , "Conscious mind" , "One's image of oneself" .)