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1. An object, such as a cork or a wad of cloth, used to fill a hole tightly; a stopper.
2. A dense mass of material that obstructs a passage.
3. A usually cylindrical or conic piece cut from something larger, often as a sample.
4. Electricity
a. A fitting, commonly with two metal prongs for insertion in a fixed socket, used to connect an appliance to a power supply.
b. A spark plug.
5. A hydrant.
a. A flat cake of pressed or twisted tobacco.
b. A piece of chewing tobacco.
7. Geology A mass of igneous rock filling the vent of a volcano.
8. Informal A favorable public mention of a commercial product, business, or performance, especially when broadcast.
9. Slang Something inferior, useless, or defective, especially an old, worn-out horse.
10. Slang A gunshot or bullet: a plug in the back.
11. A fishing lure having a hook or hooks.
v. plugged, plug·ging, plugs
v. tr.
1. To fill (a hole) tightly with or as if with a plug; stop up.
2. To insert (something) as a plug: plugged a cork in the bottle.
3. To insert in an appropriate place or position: plug a quarter into the parking meter; plugged the variables into the equation.
4. Slang
a. To hit with a bullet; shoot.
b. To hit with the fist; punch.
5. Informal To publicize (a product, for example) favorably, as by mentioning on a broadcast: authors who plug their latest books on TV talk shows.
v. intr.
1. To become stopped up or obstructed: a gutter that plugged up with leaves.
2. Informal To move or work doggedly and persistently: "You may plug along fifty years before you get anywhere" (Saul Bellow).
Phrasal Verbs:
plug in
1. To connect (an appliance) to an electrical outlet.
2. To function by being connected to an electrical outlet: a power drill that plugs in.
3. Slang To cause (someone) to use a computer network, the internet, or an electronic device.
4. Slang To become informed about or involved with: was eager to plug in to the campus social scene.
plug into
1. To connect or be connected in the manner of an electrical appliance: The local system is plugged into the national telephone network. This computer plugs into a data bank.
2. Slang To cause (someone) to use a computer network, the internet, or an electronic device.
3. Slang To cause to be informed about or involved with: connoisseurs who are plugged into the current art scene.

[Dutch, from Middle Dutch plugge.]

plug′ger n.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
References in classic literature ?
First you drill a hole in a man, and next you set about plugging the hole up."
In a plug-in hybrid electric vehicle (PHEV), battery can be recharged by plugging it into an external source of electric power.
This older ornamental Douglas fir has been treated with the plugging experiment.
This law preceded state oversight and modern plugging regulations; as a result, many wells were either improperly plugged, or not plugged at all.
Guedel also developed a little known device, the laryngeal plug (Figure 1)--this device was mounted on a tracheal catheter, and pushed between the vocal cords, thereby 'plugging' the glottis.
Whenever you''re plugging corded power tools in, be careful not to overload the socket with plugs.
Figure 21a shows a cross section of the plug and sheet at the end of the plugging step.