Cancellation includes chamber (4)
I believe the answer is:
cell
'chamber' is the definition.
(I know that cell is a type of chamber)
'cancellation includes' is the wordplay.
'includes' indicates a hidden word.
'CELL' is hidden in the letters of 'cancellation'.
(Other definitions for cell that I've seen before include "Unit of animal or plant structure" , "Prison accommodation" , "The basic structural unit of all organisms" , "Lock-up room" , "Monk's small room" .)