Religious education by foremost Vatican priest (3)
I believe the answer is:
rev
'priest' is the definition.
(short for reverend)
'religious education by foremost vatican' is the wordplay.
'religious education' becomes 'RE' (abbreviation).
'by' is a charade indicator (letters next to each other).
'foremost vatican' becomes 'v' (I am not sure about the 'foremost' bit.).
're'+'v'='REV'
Can you help me to learn more?
(Other definitions for rev that I've seen before include "Clergyman, or woman (abbr)" , "In engine-room speed up" , "Motor rotation, in short" , "Gun (an engine)" , "serviceman?" .)