Flamboyant unicorn wearing a garment (5)
I believe the answer is:
tunic
'a garment' is the definition.
(historical type of garment)
'flamboyant unicorn wearing' is the wordplay.
'wearing' indicates a hidden word (the answer is covered by or 'wearing' the clue).
'TUNIC' can be found hidden inside 'flamboyant unicorn'.
(Other definitions for tunic that I've seen before include "Partly uniform" , "Policeman may be in one" , "(Policeman's) jacket" , "Dress for soldier" , "Upper garment, for a soldier say" .)