What does "trunnion" mean?

Trunnion: (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.]