EU slang involved in a Catholic prayer (7)
I believe the answer is:
angelus
'a catholic prayer' is the definition.
(the Angelus is a Catholic prayer)
'eu slang involved' is the wordplay.
'involved' indicates an anagram (involved can mean confusing or complex).
'eu'+'slang'='euslang'
'euslang' is an anagram of 'ANGELUS'.
'in' acts as a link.
(Other definitions for angelus that I've seen before include "Short prayer" , "(Bell calling Catholics to) prayer" , "Short Catholic devotion" , "Church bell" , "Prayer at noon and 6pm" .)