Tress (4)
I believe the answer is:
curl
'tress' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for curl that I've seen before include "Hair piece; flick up" , "Spiral or coil" , "Ringlet of hair" , "Tendril of hair" , "Twist (e.g. of hair)" .)