Hold it, canon! (7)
I believe the answer is:
'hold' is the definition.
(I know that hold can be written as contain)
'it canon' is the wordplay.
'it canon' anagrams to 'CONTAIN'.
Though, I am not clear how this is indicated.
Can you help me to learn more?
(Other definitions for contain that I've seen before include "I cannot (anag) - hold back" , "Include - restrict" , "Keep the lid on" , "Carry" , "keep within bounds" .)