Former morning test (4)
I believe the answer is:
exam
'test' is the definition.
(I know that test can be written as exam)
'former morning' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'morning' becomes 'am' (as in 12:00 AM).
'ex'+'am'='EXAM'
(Other definitions for exam that I've seen before include "Written test" , "'Test, in short (4)'" , "Formal knowledge test" , "One might be taken for English" , "Test (abbr)" .)