Dismay about right eastern costume (7)
I believe the answer is:
apparel
'costume' is the definition.
(I've seen this before)
'dismay about right eastern' is the wordplay.
'dismay' becomes 'appal' (synonyms).
'about' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'eastern' becomes 'e'.
'r'+'e'='re'
'appal' placed around 're' is 'APPAREL'.
(Other definitions for apparel that I've seen before include "Pod of peas" , "Attire" , "kit" , "what's in the press?" , "it's generally put on!" .)