Keep an eye on wife at church (5)
I believe the answer is:
watch
'keep an eye on' is the definition.
('watch' can be a synonym of 'keep an eye on')
'wife at church' is the wordplay.
'wife' becomes 'w'.
'church' becomes 'ch' (common abbreviation).
'w'+'at'+'ch'='WATCH'
(Other definitions for watch that I've seen before include "Observe - guard" , "View" , "Keep under observation" , "Observe - timepiece" , "Keep an eye on - timepiece" .)