Say no more, a stunning hat (5)
I believe the answer is:
shako
'hat' is the definition.
(shako is a kind of hat)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for shako that I've seen before include "Tall military cap" , "Ceremonial hat" , "soldier's headgear" , "Plumed military cap" , "Old mil. headdress" .)