Wealthy professionals drinking super old cocktail (10)
I believe the answer is:
prosperous
'wealthy' is the definition.
(prosperous can mean wealthy or successful)
'professionals drinking super old cocktail' is the wordplay.
'professionals' becomes 'pros' ('pro' can be a synonym of 'professional').
'drinking' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'cocktail' indicates anagramming the letters.
'super'+'o'='supero'
'supero' with letters rearranged gives 'sperou'.
'pros' enclosing 'sperou' is 'PROSPEROUS'.
(Other definitions for prosperous that I've seen before include "thriving" , "Doing well" , "Rich" , "Well-to-do" , "Wealthy" .)