Why so unusually ostentatious? (5)
I believe the answer is:
showy
'ostentatious?' is the definition.
(similar in meaning)
'why so unusually' is the wordplay.
'unusually' is an anagram indicator.
'why'+'so'='whyso'
'whyso' with letters rearranged gives 'SHOWY'.
(Other definitions for showy that I've seen before include "Strikingly bright" , "Strikingly colourful" , "Ostentatious, bright" , "Flamboyant" , "Colourful, ostentatious" .)