Crow costume turned up (4)
I believe the answer is:
brag
'crow' is the definition.
(synonyms)
'costume turned up' is the wordplay.
'costume' becomes 'garb' (I've seen this before).
'turned up' says the letters should be written in reverse.
'garb' reversed gives 'BRAG'.
(Other definitions for brag that I've seen before include "game of bluff" , "Card game - boast" , "Shoot a line" , "'Show off, boast (4)'" , "game, making > boast" .)