Locks, not all permanent (4)
I believe the answer is:
mane
'locks' is the definition.
(both can mean hair)
'not all permanent' is the wordplay.
'not all' says the answer is hidden in the clue (only some of the letters).
'MANE' is hidden in the letters of 'permanent'.
(Other definitions for mane that I've seen before include "Animal neck-hair" , "Animal's neck hair" , "Name for hair on horse's neck" , "Lion or horse's 10 Across" , "Long shaggy hair" .)