Hairdo stiffener (3)
I believe the answer is:
gel
'hairdo stiffener' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gel that I've seen before include "Jelly-like substance for leg" , "Leg (anag.)" , "Colloid" , "Preparation used in setting hair" , "It may be applied to locks" .)