Isolated Greek character in society role (3,5)
I believe the answer is:
set apart
'isolated' is the definition.
(thesaurus)
'greek character in society role' is the wordplay.
'greek character' becomes 'eta' (letter from the Greek alphabet).
'in' means one lot of letters goes inside another.
'society' becomes 's' (common abbreviation in names of organisations).
'role' becomes 'part' ('part' can be a synonym of 'role').
's'+'part'='spart'
'eta' inserted inside 'spart' is 'SET APART'.
(Other definitions for set apart that I've seen before include "Isolated" , "Distinguished" , "Keep (something) for special use" , "singled out" , "Isolate" .)