from
The Collaborative International Dictionary of English v.0.48
Trunnion \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}.]
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}.
[1913 Webster]
2. (Steam Engine) A gudgeon on each side of an oscillating
steam cylinder, to support it. It is usually tubular, to
convey steam.
[1913 Webster]
{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.]
[1913 Webster]