Green’s Dictionary of Slang

1. an advertisement, a puff, esp. when filtered through a TV or radio programme.

1902		Ade Girl Proposition 50: They were friendly to the prosperous Bachelor and each one determined to put in a few quiet Plugs for Sis.
1929		Variety 10 July 1/5: The island’s hotels, the glass-bottom boats through which one views the natural aquariums, the various tours and all the rest are Wrigley owned. Everything gets a Wrigley plug for the benefit of his gum [DA].
1937		J.M. Cain Serenade (1985) 192: Better let me write those plugs.
1947		B. Schulberg Harder They Fall (1971) 143: Charlie King [...] promised us a front-page picture and a full-column plug.
1954		G. Marx letter 16 Dec. in Groucho Letters (1967) 205: Their magazine gets a free plug on my show.
1967		H.S. Thompson letter 26 June in Proud Highway (1997) 622: I gave BSA some nice plugs in my recent book on the ‘Hell’s Angels’.
1989		Viz June/July 18: Plug for LP pop record.
1999		Guardian G2 30 June 3: We are willing to give this place a plug.
2000		Indep. Rev. 11 May 11: It was time my Radio 1 show got a special kind of plug.

2. a self-aggrandizing or promoting statement.

1905		H. Green Actors’ Boarding House (1906) 370: ‘Venison, reg’lar fried kind, and deer meat a lay Auditorium,’ went on Orville, putting in a plug for his home town.
1953		T. Runyon In For Life 128: Getting in a plug about his not getting any money except what visitors tipped him.
2000		Guardian Guide 5–11 Feb. 10: Cliff has to sell his Lord’s Prayer single through word-of-mouth and plugs in churches.

3. (US black) influence.

2012

Chief Keef ‘Kobe’ 🎵 I pull them hundreds out my right pocket fifties out my left / I’m ballin’ like I’m Kobe I got plug with the ref.