Formal headgear (3,3)
I believe the answer is:
top hat
'formal headgear' is the definition.
(I've seen this in another clue)
This is the entire 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" .)