Head that may be turned (3)
I believe the answer is:
nut
'head' is the definition.
(informal term for somebody's head)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for nut that I've seen before include "'Almond or cashew, say (3)'" , "1A [CRACKPOT]?" , "needing to get tight?" , "Fan" , "something turned when making fast > food" .)