Salon stiffener (3)
I believe the answer is:
gel
'salon 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 "Become jelly-like" , "Hair-dressing preparation" , "Hair treatment" , "Leg it and get it for your hair, say" , "Mousse" .)