What sounds like standard piece of artillery? (6)
I believe the answer is:
cannon
'piece of artillery?' is the definition.
(I've seen this before)
'what sounds like standard' is the wordplay.
'what sounds like' shows a homophone (sound like).
'standard' becomes 'canon' (I've seen this before).
'canon' sounds like 'CANNON'.
(Other definitions for cannon that I've seen before include "Great gun" , "Gun - billiards' shot" , "Billiard shot in which player's ball hits the two others" , "shot playing billiards" , "Field gun" .)