Ultimately verboten to wear Speedos, say, for members of the clergy (9)
I believe the answer is:
cardinals
'for members of the clergy' is the definition.
(cardinals are senior Catholic clergymen)
'ultimately verboten to wear speedos' is the wordplay.
'ultimately' says to take the final letters.
'to wear' is an insertion indicator (to wear something is to be covered up by it).
'speedos' becomes 'car dials' (speedometers, dials on cars).
The last letter of 'verboten' is 'n'.
'n' going into 'cardials' is 'CARDINALS'.
'say' acts as a link.
(Other definitions for cardinals that I've seen before include "ones and twos?" , "Leading dignitaries" , "Birds from America" .)