Flamboyant unicyclist keeps garment (5)
I believe the answer is:
tunic
'garment' is the definition.
(historical type of garment)
'flamboyant unicyclist keeps' is the wordplay.
'keeps' says the answer is hidden in the clue.
'TUNIC' is hidden in the letters of 'flamboyant unicyclist'.
(Other definitions for tunic that I've seen before include "Close-fitting jacket that's part of a uniform" , "Belted coat" , "Smock" , "Close fitting jacket as part of uniform" , "Clobber" .)