Come between priest and one undergoing conversion (9)
I believe the answer is:
interpose
'come' is the definition.
The answer and definition can be both to do with motion as well as being verbs in their base form.
Perhaps they are linked in a way I don't understand?
'between priest and one undergoing conversion' is the wordplay.
'between' becomes 'inter'.
'priest' becomes 'p' (ecclesiastical abbreviation).
'and' means one lot of letters go next to another.
'one undergoing conversion' becomes 'ose' (I can't justify this - if you can you should give a lot more credence to this answer).
'inter'+'p'+'ose'='INTERPOSE'
Can you help me to learn more?
(Other definitions for interpose that I've seen before include "Muscle in" , "Place between" , "step in" , "Intervene between parties" , "butt in" .)