noun

1. an object used to stop up a hole, gap, outlet, etc.
2. a natural concretion or formation that stops up a passage, duct, etc.
3. a small wedge or segment cut from something, as from a melon to test its ripeness
4. 1. a cake of pressed tobacco
   2. a piece of chewing tobacco
5. an electrical connector, as with projecting prongs, designed to be fitted into an outlet, etc., thus making contact or closing a circuit
6. a kind of fishing lure
7. 1. spark plug
   2. fireplug
   3. ☆ plug hat
8. Informal a defective or shopworn article
9. ☆ Slang an old, worn-out horse
10. ☆ Informal a boost, advertisement, etc., esp. one inserted gratuitously in the noncommercial parts of a radio or TV program, magazine article, etc. for someone or something
11. Geol. igneous rock which has filled in the vent of a dead volcano and hardened: it is often exposed by erosion

Etymology: MDu plugge, a bung, plug, block, akin to Ger pflock

transitive verb plugged, plugging plug′·ging

1. to stop up or fill (a hole, gap, etc.) by inserting a plug: often with up
2. to insert a plug of (something) in a hole or gap
3. ☆ to cut a plug from (a melon) to test its ripeness
4. Informal
   1. to publicize or boost (a song) by frequent performance
   2. ☆ to advertise or publicize, esp. gratuitously in the noncommercial parts of a radio or TV program
5. Slang to shoot a bullet into
6. Slang to hit with the fist

intransitive verb

1. Informal to work or study hard and steadily; plod
2. to connect with something so as to become attached, to close an electric circuit, etc.: with into