Definition of "trunnion" [trun•nion]

• A pin or gudgeon, especially either of two small cylindrical projections on a cannon forming an axis on which it pivots. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "a point from the end equal to the semi-diameter of the trunnion, which is marked on each branch."
• "In mortar-vessels other expedients are resorted to, such as trunnion-sights, or a white line painted on the mortar-bed parallel to the axis of the bore when level; but the first plan is preferable."
• "The guns 'teams of oxen and horses were being led back into the shelter of the oaks while squads of gunners hoisted the hugely heavy cannon barrels out of their rear travelling trunnion holes and moved them into the forward fighting holes where other men used hammers to fasten the capsquares over the newly placed trunnions."