From Dutch plug, from Middle Dutch plugge (“peg, plug”), from Old Dutch *pluggi, from Proto-West Germanic *plugi. Further origin unknown. Possibly from Proto-Germanic *plugjaz, but the word seems originally restricted to northern continental West Germanic. Perhaps ultimately from the same source as Dutch plag (“cut-out sod”), itself considered to be from a substrate. Compare German Low German Plüg, Norwegian plug (“peg, wedge”, probably borrowed from Middle Low German), German Pflock (“peg”, restricted to Central German and phonetically divergent). Possibly akin to Lithuanian plúkti (“to strike, hew”).
Stack all new and fresh, composed of the fast-selling standard books only — no old plugs or unsalable books whatever.1886, The Publishers Weekly, volume 29, page 25:
Many New York booksellers promoted the impression that Quaritch had sent only 'plugs' (i.e. unsaleable books).1997, The Book Collector, volume 46, page 184:
Slang A promotion (act of promoting) of a product (such as a book, film or play) or other thing, concept, etc, for example during an interview or a commercial.
During the interview, the author put in a plug for his latest novel.
She used her televised tour of the zoo to work in another plug for conservation.
2 more examples
I just wanted to […] give a plug to Disney World […]1956 November 11, 22:37 from the start, in Franklin Heller, director, What's My Line?, season 8, episode 11, spoken by Bennett Cerf:
Department store decorations up before Thanksgiving, Christmas cards all over the place, TV full of plugs for fifty-dollar toys that inner-city kids watching can never expect to receive, parents spending what they can't afford and deluging their kids with the annual orgy of materialist values […]1973 December 8, A. Nolder Gay, “Coping With Christmas”, in Gay Community News, volume 1, number 25, page 3:
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Geography, Geology, Natural sciences A body of once molten rock that hardened in a volcanic vent. Usually round or oval in shape.
Pressure built beneath the plug in the caldera, eventually resulting in a catastrophic explosion of pyroclastic shrapnel and ash.
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Fishing, Hobbies, Lifestyle A type of lure consisting of a rigid, buoyant or semi-buoyant body and one or more hooks.
The fisherman cast the plug into a likely pool, hoping to catch a whopper.
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Agriculture, Business, Horticulture, Lifestyle A small seedling grown in a tray from expanded polystyrene or polythene filled usually with a peat or compost substrate.
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A growth of protoplasm that closes the pore openings in the cells of certain algae.
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Jewelry, Lifestyle A short cylindrical piece of jewellery commonly worn in larger-gauge body piercings, especially in the ear.
He saw me catch a trap and leave the house of a drug dealer. That's why he targeted me. He could have easily blown my ass off right then and there for lying, but for some reason he didn't. He just left. I biked back to my plug's spot and told him […]2017, Gucci Mane, Neil Martinez-Belkin, The Autobiography of Gucci Mane, page 32:
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Slang A trusted connection; someone who provides illicit goods and resources.
Add front and aft closures to the fuselage midsection. Addition or subtraction of fuselage plugs, to a maximum of five rows, conveniently distributed on each side of wing, is possible.2010, Ajoy Kumar Kundu, Aircraft Design, page 165:
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Abbreviation, Ellipsis Ellipsis of spark plug.
I changed the plugs and the coil packs.
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Abbreviation, Ellipsis Ellipsis of fireplug (“fire hydrant”).
From Dutch plug, from Middle Dutch plugge (“peg, plug”), from Old Dutch *pluggi, from Proto-West Germanic *plugi. Further origin unknown. Possibly from Proto-Germanic *plugjaz, but the word seems originally restricted to northern continental West Germanic. Perhaps ultimately from the same source as Dutch plag (“cut-out sod”), itself considered to be from a substrate. Compare German Low German Plüg, Norwegian plug (“peg, wedge”, probably borrowed from Middle Low German), German Pflock (“peg”, restricted to Central German and phonetically divergent). Possibly akin to Lithuanian plúkti (“to strike, hew”).
1
To stop with a plug; to make tight by stopping a hole.
He attempted to plug the leaks with some caulk.
2
To promote (something, especially a product or service); to mention (something) as if promoting or advertising it.
The main guest on the show just kept plugging his latest movie: it got so tiresome.
Kennedy went on nationwide speaking tour to plug environmental conservation.
1 more example
He [Mike Skinner] treats the gig as an opportunity repeatedly to plug the after-party, where he will be DJing.2019 January 26, Kitty Empire [pseudonym], “The Streets review – the agony and ecstasy of a great everyman”, in Katharine Viner, editor, The Guardian, London: Guardian News & Media, →ISSN, →OCLC, archived from the original on 08 Apr 2019:
1884, H. Rider Haggard, The Witch's Head I am awfully glad that you kept your nerve and plugged him; it would have been better if you could have nailed him through the right shoulder, which would not have killed him...