Test former spouse in the morning (4)
I believe the answer is:
exam
'test' is the definition.
('exam' can be a synonym of 'test')
'former spouse in the morning' is the wordplay.
'former spouse' becomes 'ex'.
'in the morning' becomes 'am'.
'ex'+'am'='EXAM'
(Other definitions for exam that I've seen before include "Written test" , "End-of-course assessment" , "Set of questions evaluating skill or knowledge, in short" , "Scholastic test" , "Educational test" .)