The Collaborative International Dictionary
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.]
(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.
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(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.]
Douglas Harper's Etymology Dictionary
"either of two round projections of a cannon," 1620s, from French trognon "core of fruit, stump, tree trunk," from Middle French troignon (14c.), probably from Latin truncus (see trunk).
Wiktionary
n. 1 One of the short stubby bearings on either side of a cannon; a gudgeon. 2 A similar rotational bearing comprising a rotating arc or ring sliding in the groove of a stationary arc, used in machinery to allow a workpiece to be moved relative to a fixed tool.
Wikipedia
A trunnion (from Old French "trognon", trunk) is a cylindrical protrusion used as a mounting and/or pivoting point. First associated with cannon, they are an important military development.
Alternatively, a trunnion is a shaft that positions and supports a tilting plate. This is a misnomer, as in reality it is a cradle for the true trunnion.
In mechanical engineering (see the trunnion bearing section below), it is one part of a rotating joint where a shaft (the trunnion) is inserted into (and turns inside) a full or partial cylinder.
Usage examples of "trunnion".
And they were putting trunnions on some old stuff, big things, close to a ton metal-weight but only six and eight pounders, and he hoped to get field carriages under them, too.
The barrels had to be shifted on the carriages from their travelling position into the fighting stance, then trunnions must be clamped with iron capsquares as powder and grapeshot were rammed into cold muzzles.
Once in place the gun system inserted the pintle and trunnions making the whole system ready to fire.
Their trunnions, the great knobs that held the barrels to the carriages, were being sawn through.
The barrel reared up, its trunnions tearing out of the carriage, then the heavy metal tube slowly toppled onto a wounded man.
His eyes, at the distance Sharpe was seeing them, seemed small and red, and on either side of the suspicious, questing face there sprung prominent ears that looked like the protruding trunnions either side of a cannon barrel.
Walker and Cuddy stepped close, examining it with painstaking care from the thick breech down through the trunnions and the extra foot of spongy, pitted metal at the muzzle.
Heavy masses of metal chinged, then clanged loudly together—the trunnions of a 15-cm plasma cannon dropping into the cheek pieces.
To obviate this danger, and to be able to force out the load, it would be necessary, perhaps, to return to the process of the fourteenth century, hooping, and to strengthen the piece exteriorly, by a succession of steel rings unsoldered, from the breech to the trunnion.
The Tainter gates were huge curved steel doors fifty feet high and forty-two feet wide, with support struts in the middle that attached the gates to trunnion pins on each side.
There was another catwalk forty feet below him, at the same level as the trunnion pins on which the Tainter gates pivoted.