Italian leader supporting the Spanish priest (3)
I believe the answer is:
eli
'priest' is the definition.
(I've seen this before)
'italian leader supporting the spanish' is the wordplay.
'leader' suggests taking the first letters.
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'the spanish' becomes 'el'.
The initial letter of 'italian' is 'i'.
'i' after 'el' is 'ELI'.
(Other definitions for eli that I've seen before include "- Wallach, US actor" , "Distort then untruth to get a Biblical character" , "Priest, teacher of Samuel" , "Old Testament high priest" , "Man" .)