Quantity of opium churchwarden can consume? (7)
I believe the answer is:
pipeful
'quantity' is the definition.
(pipeful is a kind of quantity)
'opium churchwarden can consume?' is the wordplay.
I cannot quite understand how this works, but
'churchwarden' could be 'pipe' (I've seen this in other clues) and 'pipe' is found within the answer.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for pipeful that I've seen before include "amount of tobacco?" , "quid" .)