What a pupil did in the dark (7)
I believe the answer is:
dilated
'dark' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'what a pupil did in' is the wordplay.
'what a pupil' becomes 'late' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'late' going within 'did' is 'DILATED'.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for dilated that I've seen before include "Widened; expanded" , "Made more open/wide" , "Became more open" , "Enlarged" , "Made more open" .)