Uncle Sam headgear (3,3)
I believe the answer is:
top hat
'uncle sam 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 "Man's cylindrical headgear" , "Formal headgear for man" , "Lofty male headgear for posh occasions" , "14 headgear" , "Kind of headgear, goes with 28 down" .)