Fashion leaders in Ascot outfits look stunning too (4)
I believe the answer is:
also
'too' is the definition.
(synonyms)
'fashion leaders in ascot outfits look stunning' is the wordplay.
'fashion' indicates an anagram.
'leaders in' indicates taking the first letters.
The initial letters of 'ascot outfits look stunning' is 'aols'.
'aols' with letters rearranged gives 'ALSO'.
(Other definitions for also that I've seen before include "What's more" , "Old" , "an indication of more to come" , "'Besides, moreover (4)'" , "To boot" .)