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1. Any of several structures that project from the side of a boat or ship, especially a gun platform.
2. A short, curved, air-filled projection on the hull of a seaplane, imparting stability in the water.

[Perhaps alteration of expansion.]


1. (Nautical Terms) navy an outboard support for a gun enabling it to fire fore and aft
2. (Firearms, Gunnery, Ordnance & Artillery) a semicircular gun turret on the side of a tank
3. (Nautical Terms) a float or flotation chamber along the gunwale of a boat or ship
4. (Nautical Terms) a structural projection from the side of a paddle steamer for supporting a paddle wheel
5. (Aeronautics) a structural unit attached to a helicopter fuselage by fixed struts, housing the main landing gear and inflatable flotation bags
[C19: perhaps from expansion]


(ˈspɒn sən)

1. a structure projecting from the side or main deck of a vessel, as one supporting a gun.
2. a buoyant appendage at the gunwale of a canoe to resist capsizing.
[1830–40; earlier also sponsing, sponcing, of uncertain orig.]
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References in periodicals archive ?
The NBC protection system has been moved in the rear left sponson, the right one being used to accommodate equipment.
The crew reported that the NBC OVERHEAT SPONSON OUT light didn't provide any warning.
The 75-millimeter gun mounted on the right sponson was removed, the hole was sealed, and the space was allotted for internal storage of the 425 gallons of fuel required to operate the flamethrower.
As he went by his starboard sponson (a projection on the side of the boat) lifted out of the water then dropped back as he continued at an unbelievable speed, and almost immediately Bluebird took off, somersaulted and crashed.
He said: "Llandudno inshore lifeboat took a portable pump, and put a crewman and the pump on board the trimaran to keep the water level on the damaged sponson down until we could make the boat safe.
Screw wash from the port screw during the port-twist maneuver had caused water to flow over the RHIB's sponson, and the craft capsized.
Everything outside the tank was shot up, the 50-caliber machine gun, the sponson boxes, mufflers, and radio antenna, but the tank did not burn.
The next thing I remember was someone on another sponson throwing me a life ring, which landed about five feet from the hull of the ship.
Did this trash come up from a sponson or from someone being careless?
Where liberals think the guarantee of rights a sponson which alone steadies and constrains the state morally, nationalists decry it as far too thin and too formal a basis for polity.
ITT Exelis delivered first helicopter sponson on the CH-53K program in November 2010 (Photo: ITT Exelis)
Following installation of the last sponson, we can start the countdown to refloating and final departure of the wreck," Michael Thamm, chief executive of Costa Cruises, a unit of the liner's owner Carnival Corp, said in the statement.