Boast about dress (4)
I believe the answer is:
brag
'boast' is the definition.
(brag is a kind of boast)
'about dress' is the wordplay.
'about' is a reversal indicator.
'dress' becomes 'garb' (synonyms).
'garb' in reverse letter order is 'BRAG'.
(Other definitions for brag that I've seen before include "Shoot a line" , "Boast about garb" , "Card game - boast" , "game, making > boast" , "Show off, crow" .)