Expert on initiation of ministerial staff (4)
I believe the answer is:
mace
'staff' is the definition.
(a mace is a ceremonial staff or stick)
'expert on initiation of ministerial' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'on' means one lot of letters go next to another.
'initiation of' indicates taking the first letters.
The first letter of 'ministerial' is 'm'.
'ace' after 'm' is 'MACE'.
(Other definitions for mace that I've seen before include "Spiked club" , "Came to get ancient weapon" , "put on the rack?" , "One of 9 [CLUBS]" , "Spice; ceremonial baton" .)