1. A cylindrical projection on each side of a piece, whether gun, mortar, or howitzer, serving to support it on the cheeks of the carriage.
2. (Science: engineering) A gudgeon on each side of an oscillating steam cylinder, to support it. It is usually tubular, to convey steam. Trunnion plate, a ring on a cannon next before the trunnions.
Origin: OF. Trognon the stock, stump, or truck of a tree, F. Trognon a core, stalk, fr.tron a trunk, stem. Cf. Trunk.