Formal headwear (3,3)
I believe the answer is:
top hat
'formal headwear' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for top hat that I've seen before include "Formal headgear of lofty sort" , "Man's headgear worn with formal dress" , "It's seen with tails" , "Old film" , "Head gear" .)