Trun"nion (?), n. [OF. trognon the stock, stump, or truck of a tree, F. trognon a core, stalk, fr.tron a trunk, stem. Cf. Trunk.]
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. [R.]
© Webster 1913.