Big old gun member of the clergy picked up (6)
I believe the answer is:
cannon
'big old gun' is the definition.
'cannon' can be an answer for 'gun' (cannon is a kind of gun). I'm unsure of the 'big old' bit.
'member of the clergy picked up' is the wordplay.
'member of the clergy' becomes 'canon' (I've seen this before).
'picked up' indicates a 'sounds like' (homophone) clue.
'canon' sounds like 'CANNON'.
Can you help me to learn more?
(Other definitions for cannon that I've seen before include "Large wheeled gun" , "The large gun sounds like a church dignitary" , "Field gun" , "Heavy artillery gun" , "Large artillery gun" .)