plug

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

• noun An object, such as a cork or a wad of cloth, used to fill a hole tightly; a stopper.
• noun A dense mass of material that obstructs a passage.
• noun A usually cylindrical or conic piece cut from something larger, often as a sample.
• noun A fitting, commonly with two metal prongs for insertion in a fixed socket, used to connect an appliance to a power supply.
• noun A spark plug.
• noun A hydrant.
• noun A flat cake of pressed or twisted tobacco.
• noun A piece of chewing tobacco.
• noun Geology A mass of igneous rock filling the vent of a volcano.
• noun Informal A favorable public mention of a commercial product, business, or performance, especially when broadcast.
• noun Slang Something inferior, useless, or defective, especially an old, worn-out horse.
• noun Slang A gunshot or bullet.
• noun A fishing lure having a hook or hooks.
• intransitive verb To fill (a hole) tightly with or as if with a plug; stop up.
• intransitive verb To insert (something) as a plug.
• intransitive verb To insert in an appropriate place or position.
• intransitive verb To hit with a bullet; shoot.
• intransitive verb To hit with the fist; punch.
• intransitive verb Informal To publicize (a product, for example) favorably, as by mentioning on a broadcast.
• intransitive verb To become stopped up or obstructed.
• intransitive verb Informal To move or work doggedly and persistently.

from The Century Dictionary.

• To stop with a plug; make tight by stopping a hole: as, to plug a decayed tooth; to plug a wound with lint.
• To hit with a ball or bullet: as, to plug a buck with a rifle.
• To cut out a plug from: said of watermelons when a tapering plug is cut out to see if the fruit is ripe, and then replaced.
• noun In geology, a cylindrical mass of lava, a remnant of the last eruption from a volcanic vent, which chilled in the conduit and plugged it up. See neck, 6 , and stock, 35.
• noun A book that does not sell at all.
• noun In stone-cutting, a wedge which is driven into a hole that has been drilled in a stone for the purpose of splitting it. For large pieces of stone a series of holes is drilled and a wedge or plug driven into each.
• noun In a steam-engine: A plug-rod; a plug-frame.
• noun A safety-plug; a fusible plug inserted in a boiler and made of some alloy which will melt if the temperature of the metal plate of the shell rises above a certain point by reason of low water.
• noun Same as peg, 7.
• noun A piece of wood or other substance, usually in the form of a peg or cork, used to stop a hole in a vessel; a stopple; a bung or stopper of any kind.
• noun A peg, wedge, or other appliance driven in, or used to stop a hole or fill a gap. ,
• noun A wedge-pin forced between a rail and its chair on a railway.
• noun A spigot driven into place, as in a barrel, in contradistinction to one screwed in.
• noun A wooden stopper fitted in the opening of the pump on a ship's deck during a storm, to protect the water-tanks against lightning; a pump-stopper.
• noun A small piece of some substance, as metallic foil, used by a dentist to fill the cavity of a decayed tooth.
• noun A branch pipe from a watermain, leading to a point where a hose can be conveniently attached, and closed by a cap or plug; a fire-plug.
• noun In die-sinking, a cylindrical piece of soft steel the end of which is fitted to a matrix.
• noun A flat oblong cake of pressed tobacco.
• noun A man's silk or dress hat; a plug-hat.