Artillery piece (6)
I believe the answer is:
cannon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">artillery piece</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cannon that I've seen before include "Weapon firing large balls" , "Heavy ordnance" , "One of the big guns" , "Big shot" , "Gun - billiards' shot" .)