Idiot can't supply reading material (9)
I believe the answer is:
dictation
'reading material' is the definition.
(material that is read aloud or dictated)
'idiot can't supply' is the wordplay.
'supply' indicates an anagram (in a supple way).
'idiot'+'cant'='idiotcant'
'idiotcant' with letters rearranged gives 'DICTATION'.
(Other definitions for dictation that I've seen before include "Speech for transcribing" , "Speaking of words to be taken down" , "office activity" .)