King mislaid crown before midday inspection (4)
I believe the answer is:
exam
'king mislaid crown' is the definition.
I can't tell whether this defines the answer.
'before midday inspection' is the wordplay.
'before' becomes 'e' (I've seen this in other clues).
'midday inspection' becomes 'xam' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'e'+'xam'='EXAM'
Can you help me to learn more?
(Other definitions for exam that I've seen before include "Oral maybe" , "Written test" , "One test" , "(Academic) test" , "Test (abbrev.)" .)