Green’s Dictionary of Slang

(a) to spend money or bet recklessly, to speculate heavily, to run into debt.

1875		N.Y. Times 6 July 2/2: The heavy speculators plunged heavily upon [a race horse].
1883		E.J. Milliken Childe Chappie’s Pilgrimage 55: To me it’s all confounded slow, / Mashing and plunging, love and thirst.
1887		Lantern (N.O.) 9 July 2: If he don’t quit plunging into the watered stock of Haley’s he’ll get his empty head bumped so hard for ice cream and cakes that he’ll have to tumble to the racket.
1890		‘Doss Chiderdoss’ ‘The Rejected’ Sporting Times 29 Mar. 1/3: He plunged upon Sweetbriar, who, he said, was quite a flyer.
1894		Truth (Sydney) 23 Dec. 1/7: I will not plunge [...] but here goes. I’ll put a fiver on one horse for the first race.
c.1895		F. Norris Vandover and the Brute (1914) 250: Then they began to ‘plunge,’ agreeing to play a no-limit game.
1898		Binstead & Wells A Pink ’Un and a Pelican 31: Harry, what d’yer say if we goes upstairs for a bit an’ sees this chap a-plungin’.
1900		Nat. Police Gaz. (NY) 24 Mar. 6/1: [T]he plunging banker [...] was losing.
1901		D. Cotsford Society Snapshots 104: It was all through that brute of a mare . . .she plunged — I mean I plunged — and lost my neck . . . I mean she lost be a head.
1902		‘The Wasp’ ‘Tales of the Penance Track’ in Bulletin (Sydney) 31 May 31/2: Riley [...] plunged on Revenue to the extent of ten plugs.
1917		‘Banjo’ Paterson ‘The Downfall of Mulligan’s’ in Three Elephant Power 62: The priest and the young squatter won slightly; this was part of the plan to lead them on to plunge.
1922		Joyce Ulysses 255: – Sceptre will win in a canter, he said. – I plunged a bit, said Boylan winking and drinking.
1923		Wodehouse Inimitable Jeeves 145: It wouldn’t do to plunge unless you’re sure.
1932		F. Jennings Tramping with Tramps 180: Recklessly I plunged the lot for a meal of ‘sausage and mash’.
1938		H. Asbury Sucker’s Progress 440: Any responsible player who wanted to plunge could always go higher by applying to Canfield.
1940		D. Maurer Big Con 17: The atmosphere is one of reckless plunging and betting.
1952		W. Winchell On Broadway 9 Sept. [synd. col.] Jerry Brady [...] counseled an actor he saw plunging at the $50 window.
1959		W. Burroughs Naked Lunch 150: They are lousy gamblers plunge in a losing streak and hedge when they win.
1965		(con. 1940s) Malcolm X Autobiog. (1968) 207: Every weekend I’d pay my bill — anywhere from fifty to even one hundred dollars, if I had really plunged on some hunch.
1966		J. Holledge Great Aust. Gamble 26: That day, however, he plunged and by the last race had built his bank to £3,000.
1969		B. Jackson Thief’s Primer 164: He got to plunging at the VFW hall and places like that where they have a lot of gambling.

(b) to perform anything intensely.

2001

N. Barlay Hooky Gear 85: He plunge a brandy, bang his glass down an start to fill us all up.

(a) to kill, to murder.

1995

J. Cameron Vinnie Got Blown Away 71: Lucky he never got plunged even for what was up his back pocket.

(b) to stab.

1998		J. Hoskison Inside 34: Plungin’s a stabbin’.
2000		J.J. Connolly Layer Cake 153: Plunged him in the throat, straight in the fuckin jugular.
2012		(con. 1980s) I. Welsh Skagboys 146: Ah jist plunged the radge a couple ay times, gie um something tae fuckin well think aboot.