In which cast hears Lear, perhaps (9)
I believe the answer is:
rehearsal
'in which cast' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'hears lear perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'hears'+'lear'='hearslear'
'hearslear' with letters rearranged gives 'REHEARSAL'.
Can you help me to learn more?
(Other definitions for rehearsal that I've seen before include "Practice - run-through" , "Play run-through" , "Practice session in preparation for public performance" , "Preparation for a show" , "Dummy run" .)