Wife leaving joiner for church officer (5)
I believe the answer is:
Here is my best explanation:
'church officer' is the definition.
(elder is a kind of church officer)
I cannot understand how the remainder of the clue works.
(Other definitions for elder that I've seen before include "Senior - church official", "Patriarch", "Older or two", "Ancestor", "Kind of tree or sage person", "Shrub - senior", "Senior member of a tribe", "Tree - wise counsellor", "Older person - one's senior" and "Senior type of tree?".)