Test no longer taking half a day (4)
I believe the answer is:
Here is my best explanation:
'test' is the definition.
('exam' can be a synonym of 'test')
'no longer taking half a day' is the subsidiary indication.
'no longer' becomes 'ex'.
'taking' is a charade indicator (letters next to each other).
'half' suggests halving the letters.
'day' becomes 'mon'.
'amon' with half the letters taken is 'am'.
(Other definitions for exam that I've seen before include "One might be taken for English", "One taken by candidate", "paper", "End-of-course assessment", "Formal knowledge test", "Important test", "Written test", "Test of knowledge", "Brief test" and "Scholastic test".)