Robert's hairstyle (3)
I believe the answer is:
bob
This clue is a double definition.
'robert's' is the first definition.
(short for Robert)
'hairstyle' is the second definition.
(bob is a kind of hairstyle)
(Other definitions for bob that I've seen before include "Pre-decimal coin" , "Bounce" , "Quick curtsy" , "line of verse" , "Bow" .)