Brimless headgear (5)
I believe the answer is:
beret
'brimless headgear' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for beret that I've seen before include "Soldier's cap" , "Basque headgear" , "French-style hat" , "Felt hat" , "Flattish felt cap" .)