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 Same as catamaran, 4.
• 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.

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 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.
• 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.

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