Chiefly in pl. Also 7–9 trunion, 8 tronion. [ad. F. trognon core of fruit, stump, trunk of a tree (14th c. in Godef., Compl.); of uncertain origin.]
1. Each of a pair of opposite gudgeons on the sides of a cannon, upon which it is pivoted upon its carriage. (Disused in large modern guns.)
a. 1625. Nomenclator Navalis (Harl. MS. 2301). Trunnions are those knobbs which come from the side of the Ordnance and doe beare them vpp vpon the Cheekes of the Carriages.
1690. J. Mackenzie, Siege London-Derry, 17/1. The rest attending the Lord Kingston till they had broke the Trunnions, and nailed the heavier Guns.
1781. Justamond, Priv. Life Lewis XV., III. 389. They broke off the trunnions of the canon.
1794. Nelson, in Nicolas, Disp. (1845), I. 430. The Agamemnon’s two twenty-four pounders are both ruined: one split up to the rings; the other with the trunnion knocked so much off, that it is useless for shot.
1890. W. J. Gordon, Foundry, 26. One of the strangest of the very latest developments of modern gunnery is the abolition of the trunnions.
b. Each of any similar pair of opposite pins or pivots on which anything is supported; spec. in the oscillating steam-engine, a hollow gudgeon on each side of the cylinder, upon which it is pivoted, and through which the steam passes into and out of the cylinder; also, a single projecting pivot.
1727. Bradley’s Fam. Dict., s.v. Chimney, They fit two Trunnions or knobs to the Middle of this Swipe.
1831. J. Holland, Manuf. Metal, I. 88. The centre of the pivots or trunnions on which it [the large metal helve] works. Ibid. (1833), II. 215. The bar-handle acting … upon a fulcrum or mouth-piece of solid iron, the top of which works against a trunnion under the middle of the press head.
1867. J. Hogg, Microsc., I. ii. 82. The tripod-stand gives a firm support to the trunnions.
1873. W. S. Mayo, Never Again, xxii. This vessel I shall hang on trunnions, and keep in constant revolution while the glass is in a liquid state.
1895. Model Steam Engine, 21. In a real engine, the centres on which the cylinders oscillate are called trunnions.
† c. transf. A pin or peg of wood; a treenail. Obs. rare.
1627. Capt. Smith, Seaman’s Gram., ii. 4. Those plankes are made fast with good Treenailes and Trunnions of well seasoned timber.
2. attrib. and Comb., as trunnion-hole, -joint, -lathe, -piece, -pin; trunnion-band, the band on which the trunnions are fixed; trunnion-box, a metal case fixed over the trunnion to prevent the gun leaving the carriage; trunnion-carriage, the top carriage of a mortar (Webster, 1911); trunnion-chain, a chain for slinging a cannon by the trunnions (ibid.); trunnion-cradle, branching arms in certain gun-carriages, in the extremities of which the trunnions play (ibid.); trunnion-ledge, -level, a small ledge on the trunnion of a heavy gun, parallel with the axis, as a guide to the elevation or depression of the piece (Cent. Dict. Suppl., 1909); trunnion-plate, an iron plate on the cheek of a wooden gun-carriage, on which the trunnion plays; also, a strengthening shoulder reinforcing the trunnion (Cent. Dict., 1891); trunnion-ring, the raised band or molding encircling a cannon a little in front of the trunnions; trunnion-rule, an instrument for determining the distance from the trunnions to the base-ring (Cent. Dict. Suppl.); trunnion-sight, a front sight placed on the trunnion-band; trunnion-square, an instrument for determining whether the trunnions are perpendicular to the axis of the gun; trunnion-valve, a steam-valve situated in or attached to the trunnion of an oscillating cylinder.
1812. Wellington, in Gurw., Desp. (1838), IX. 131. It is recommended by the officers of the artillery that they should be fitted with strong iron *trunnion boxes, to secure the guns.
1795. Burke, Lett. to Ld. Auckland, Wks. IX. p. xxii. Those planks of tough and hardy oak, that used for years to brave the buffets of the Bay of Biscay, are now turned, with their warped grain and empty *trunnion-holes, into very wretched pales.
1859. F. A. Griffiths, Artill. Man., Plate (1862), 112. Trunnion hole.
1876. Routledge, Discov., 14. The *trunnion joints are easily packed, so that no leakage takes place.
1877. Knight, Dict. Mech., *Trunnion-lathe, a machine tool for turning off the trunnions of ordnance or oscillating steam-cylinders.
1859. F. A. Griffiths, Artill. Man. (1862), 190. The *trunnion piece is made from a solid forging, and after being bored and turned, is shrunk in its place on the gun.
1888. Hasluck, Model Engin. Handybk. (1900), 27. The upper hole … takes the trunnion or pin on which the cylinder oscillates. Fig. 13 shows this *trunnion pin.
1644. Nye, Gunnery (1670), 42. The Base-ring, the *Trunnion-ring, or Rings.
1868. Rep. to Govt. U.S. Munitions War, 81. The Whitworth gun … is manufactured of one material (except the trunnion-ring).
Hence Trunnioned a., provided with trunnions (Webster, 1864); Trunnionless a., having no trunnions.
1877. Times, 19 Nov., 10/5. On the stacks of timber thus raised iron girders are to be laid, on which the trunnioned monolith [Cleopatra’s needle] is to be swung, under the control of guy ropes.
1855. Belfast News-letter, 3 Nov., 4/6. You come upon ill-treated cannon, trunnionless some, others with muzzles knocked off, [etc.].
1890. W. J. Gordon, Foundry, 26. A trunnionless gun has a curious crippled look about it.
