Test late in the morning (4)
I believe the answer is:
exam
'test' is the definition.
(I know that test can be written as exam)
'late in the morning' is the wordplay.
'late' becomes 'ex' (prefix meaning former or onetime).
'in the morning' becomes 'am' (AM on a clock).
'ex'+'am'='EXAM'
(Other definitions for exam that I've seen before include "Test (abbr)" , "In brief, a test as in school" , "Student test" , "Something to sit" , "School test (colloq.)" .)