Fool hiding small kink (5)
I believe the answer is:
twist
'kink' is the definition.
(I know that kink can be written as twist)
'fool hiding small' is the wordplay.
'fool' becomes 'twit' (both can mean a stupid person).
'hiding' indicates putting letters inside.
'small' becomes 's' (abbreviation - e.g. clothes size).
'twit' placed around 's' is 'TWIST'.
(Other definitions for twist that I've seen before include "Wring" , "Twine, coil" , "Screw; distort" , "Wind spirally" , "Convolute" .)