Definition of trunnion in US English:



  • 1A pin or pivot forming one of a pair on which something is supported.

    • ‘Although the compass carries no maker's marks, it is designed to fit across the transit's trunnions and has a pin that fits a hole on the transit.’
    • ‘The bearings for lower shaft consist of solid bushings fastened into trunnion, and are provided with oil-chamber and capillary felt, making them practically self-oiling and dust-proof.’
    • ‘The receiver is thicker, and it has a reinforced trunnion.’
    • ‘The main frame of this machine is fitted at its base with trunnions, which work in a foundation plate.’
    • ‘The introduction of trunnions, the pivots in the middle of the barrel permitting it to move independently of the carriage, was a simple but important development.’
    central shaft, fulcrum, axis, axle, swivel, pin, hub, spindle, hinge, pintle, kingpin, gudgeon
    View synonyms
    1. 1.1 A supporting cylindrical projection on each side of a cannon or mortar.
      • ‘At the top of the platform, the turntable and trunnions of the gun mount are still there, but the anti-aircraft machine guns are gone.’
      • ‘The barrel and breech have been salvaged, so all that remains at the top are a pair of trunnions.’
      • ‘As with the machine-gun platform, the turntable and trunnions are intact, but the gun itself is missing.’
      • ‘The gun is fitted with a trunnion mounted telescopic sight for direct firing up to 3,000m.’


Early 17th century: from French trognon ‘core, tree trunk’, of unknown origin.