Indifference shown by a nincompoop turning head (9)
I believe the answer is:
aloofness
'indifference' is the definition.
(aloofness is a kind of indifference)
'a nincompoop turning head' is the wordplay.
'nincompoop' becomes 'fool' (I've seen this before).
'turning' shows that the letters should be reversed in order.
'head' becomes 'ness' (ness is a headland).
'fool' in reverse letter order is 'loof'.
'a'+'loof'+'ness'='ALOOFNESS'
'shown by' is the link.
(Other definitions for aloofness that I've seen before include "Haughty nature" , "Indifference by personal withdrawal" , "Indifference, reserve" , "Detachment" , "Cool and distant manner" .)