pontoon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A floating structure, such as a flatbottom boat, used to support a bridge.
• noun A floating structure serving as a dock.
• noun Either of two floating structures attached to a seaplane.

from The Century Dictionary.

• noun In milit engin., a flat-bottomed boat, or any light framework or floating structure, used in the construction of a temporary bridge over a river.
• noun Nautical, a lighter; a low flat vessel resembling a barge, furnished with cranes, capstans, and other machinery, used in careening ships, chiefly in the Mediterranean.
• noun In hydraulic engineering: A water-tight structure or frame placed beneath a submerged vessel and then filled with air to assist in refloating the vessel.
• noun A water-tight structure which is sunk by filling with water and raised by pumping it out, used to close a sluiceway or entrance to a dock. Also spelled ponton.
• noun In anatomy, a loop or knuckle of the small intestine: so called from the way it appears to float in the abdominal cavity. See the quotation under mesentery.
• noun In brewing, one of the cleansing-rounds or cleansing-squares used for clarifying ale.
• noun Same as catamaran, 4.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Mil.) A wooden flat-bottomed boat, a metallic cylinder, or a frame covered with canvas, India rubber, etc., forming a portable float, used in building bridges quickly for the passage of troops.
• noun (Naut.) A low, flat vessel, resembling a barge, furnished with cranes, capstans, and other machinery, used in careening ships, raising weights, drawing piles, etc., chiefly in the Mediterranean; a lighter.
• noun a bridge formed with pontoons.
• noun the carriages of the pontoons, and the materials they carry for making a pontoon bridge.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun military A flat-bottomed boat used as a support for a temporary bridge.
• noun A floating structure supporting a bridge or dock.
• noun A box used to raise a sunken vessel.
• noun A float of a seaplane.
• noun card games A card game in which the object is to obtain cards whose value adds up to, or nearly to, 21 but not exceed it.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a float supporting a seaplane
• noun (nautical) a floating structure (as a flat-bottomed boat) that serves as a dock or to support a bridge