Formal headgear (3,3)
I believe the answer is:
top hat
'formal headgear' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for top hat that I've seen before include "Wear it with tails" , "14 headgear" , "Stylish film" , "Formal attire" , "Formal head-wear for a man" .)