1620s, originally a seamen's term, probably from Dutch plug, Middle Dutch plugge "bung, stopper," related to Norwegian plugg, Danish pløg, North Frisian plaak, Middle Low German pluck, German Pflock; ultimate origin uncertain. Irish and Gaelic words are from English. Sense of "wad or stick of tobacco" is attested from 1728, based on resemblance. Electrical sense is from 1883, based on being inserted; meaning "sparking device in an internal combustion engine" is from 1886. Meaning "advertisement" first recorded 1902, American English, perhaps from verb sense "work energetically at" (c.1865).
"close tightly (a hole), fill," 1620s, from plug (n.) or from Dutch pluggen. Meaning "work energetically at" is c.1865. Sense of "popularize by repetition" is from 1906. Slang sense "put a bullet into" is recorded from 1870. Related: Plugged; plugging.
A dense mass of material filling a hole or closing an orifice. v. plugged, plug·ging, plugs
To fill tightly with a plug.
[perhaps fr Dutch plug, ''a sorry nag,'' related to Swiss-German pflag and to Danish plag, ''foal'']
(also plugged)Worthless; phony: And furthermore the author does not give a plug damn (1888+)
[all senses fr the notion of plug as hole-filler; the second sense may be influenced by the notion of inferiority in plug1]
Positive publicity: I certainly would appreciate him giving me a plug with the owners (1902+)
[fr Oxford University slang, apparently in imitation of heavy ploddingsteps,orperhapsthestepsofanoldandtired horse; sense of selling or advocating fr the fact that such commendation was originally constant and repetitive]