Coyish eight agitated upper classes (4,7)
I believe the answer is:
high society
'upper classes' is the definition.
(thesaurus)
'coyish eight agitated' is the wordplay.
'agitated' indicates an anagram.
'coyish'+'eight'='coyisheight'
'coyisheight' is an anagram of 'HIGH SOCIETY'.
(Other definitions for high society that I've seen before include "Nineteen fifty six Grace Kelly film" , "Bing Crosby/Grace Kelly musical" , "Fashionable elite" , "Crosby/Sinatra film" , "Crosby/Kelly/Sinatra film" .)