Trunnion

n.	1.	(Gun.) A cylindrical projection on each side of a piece, whether gun, mortar, or howitzer, serving to support it on the cheeks of the carriage. See Illust. of Cannon.
	2.	(Steam Engine) A gudgeon on each side of an oscillating steam cylinder, to support it. It is usually tubular, to convey steam. Trunnion plate (Gun.) a plate in the carriage of a gun, mortar, or howitzer, which covers the upper part of the cheek, and forms a bearing under the trunnion. Trunnion ring (Gun.) a ring on a cannon next before the trunnions.