Like unwashed hair (4)
I believe the answer is:
oily
'like unwashed hair' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oily that I've seen before include "Oleaginous" , "Viscous" , "Smoothly ingratiating" , "Smarmy" , "Smooth; like lubricant" .)