Sister protected by European Union (3)
I believe the answer is:
nun
'sister' is the definition.
(thesaurus)
'protected by european union' is the wordplay.
'protected by' indicates the answer is hidden within the clue.
'NUN' is hidden within 'european union'.
(Other definitions for nun that I've seen before include "She's a member of a religious community" , "whose son entered Promised Land" , "Priory female" , "religious person" , "Holy sister" .)