Mother joins church staff (4)
I believe the answer is:
mace
'staff' is the definition.
(mace is a kind of staff)
'mother joins church' is the wordplay.
'mother' becomes 'ma' (ma is a kind of mother).
'joins' means one lot of letters go next to another.
'church' becomes 'ce' (abbreviation for Church of England**).
'ma'+'ce'='MACE'
(Other definitions for mace that I've seen before include "One of 9 [CLUBS]" , "Tear gas - spice" , "Staff - ground nutmeg" , "Spice; ceremonial baton" , "Came to get nutmeg spice" .)