Green’s Dictionary of Slang

1. a large sum, a fortune.

1767

J. Wedgwood in Life (1894) 102: He is in no danger of making a Plunk, or what would be esteemed a Fortune by any other than a little country manufacturer .

2. (US, also plunker) a dollar; thus in pl., money in general.

1885		Donaldsville Chief (LA) 26 Sept. 1/5: Idle capital to the amount of twenty-eight plunkers was not floating around as promiscuously as before.
1888		A. Trumble Mott Street Poker Club 27: Five bright, new silver dollars were shaken from his venal grasp [...] ‘Collar the plunks, Chinay,’ shouted Finnegan.
1891		W. De Vere ‘An Angel’s Visit’ Tramp Poems 35: Here’s five ‘plunkers’ cold.
1893		S. Crane Maggie, a Girl of the Streets (2001) 38: What’s deh use! Yeh’ll git pulled in! Ev’rybody ’ill be onto it! An’ ten plunks! Gee!
1900		Flynt & Walton Powers That Prey 62: It cost his push a thousand plunks to spring him from the coppers.
1902		J.D. Corrothers Black Cat Club 43: You gits nine plunkers a week.
1905		‘Hugh McHugh’ You Can Search Me 28: It’s good for a thousand plunks apiece every week.
1906		C. M’Govern Sarjint Larry an’ Frinds 36: A pension of twenty plunkers a month.
1906		S. Ford Shorty McCabe 80: The family had been in the nobility business so long that the pedigree had lasted out the plunks.
1910		O. Johnson Varmint 66: One plunk’s enough.
1911		S. Ford Torchy 236: But what checks? [...] The five thousand plunkers to Mutt & Mudd?
1914		S. Lewis Our Mr Wrenn (1936) 21: Some land that my Dad left me has sold for nearly a thousand plunks.
1925		Dos Passos Manhattan Transfer 204: Us kids used to think it was paradise if we had five plunks to take a couple of girls down to the Island.
1931		O. Strange Law O’ The Lariat 203: He warn’t the sort o’ man to pass up most of two thousand plunks.
1954		R. Service ‘Violet de Vere’ in Carols of an Old Codger 55: ‘There’s twenty plunks to pay my fine, – but now I come to think: / Judge, darlin’ you’ve been owin’ me five bucks for near a year: / Take fifteen, – there! We’ll call it square,’ said Violet de Vere.

3. a blow, a hit.

1905		Marvel III:58 31: A heavy plunk followed, as though a ton weight had been dropped suddenly.
1910		Marvel 15 Oct. 16: He struck me on the head [...] then gave me a plunk in the face.
1932		(con. 1910s) J.T. Farrell Young Lonigan in Studs Lonigan (1936) 10: And many’s the plunk in the cocoanut that Paddy Lonigan got.