A church vault (3)
I believe the answer is:
arc
'vault' is the definition.
The definition and answer can be both to do with motion as well as being verbs in their base form.
Perhaps you can see an association between them that I can't see?
'a church' is the wordplay.
'church' becomes 'RC' (abbreviation for Roman Catholic).
'a'+'rc'='ARC'
Can you help me to learn more?
(Other definitions for arc that I've seen before include "Section of circumference" , "Curvature" , "part of turning circle?" , "development of plot" , "Part of a circular line" .)