Green’s Dictionary of Slang

1. a whore.

c.1665		‘Lampoon’ Harleian Mss. 6913.193: Plumpers Firk’t it with Prince Perkin.
1765		H. Howard Choice Spirits Museum 65: Plumpers skulk at Hick’s-Hall.

2. a (large) female breast.

1731		Swift ‘Beautiful Young Nymph Going to Bed’ in Chalmers Eng. Poets XI (1810) 502/1: Corrinna wakes. A dreadful sight! [...] A wicked rat her plaster stole, Half eat, and dragg’d it to his hole. [...] And puss had on her plumpers p-ssed.
1772		Bridges Burlesque Homer (3rd edn) 123: Unless I dress your plumpers out, / And rigg you for a ball or rout, / There’s ne’er a rake in all the town / Would tip you half of half a crown.

3. a heavy blow; also fig. use.

1772		Bridges Burlesque Homer (3rd edn) 378: Gave me a plumper on the jaw, / And cry’d; Pox take you!
1784		Rambler’s Mag. June 209/1: The Jew [...] received on his left eye the plumper, intended for his master.
1796		Sporting Mag. June VIII 145/2: The other lady [...] called her antagonist by the filthy name of b—, which was immediately followed by a plumper just under the right eye.
1804		Sporting Mag. Mar. XXIII 352/1: So, damn it, Jack hit him a crack. / Well said, my boy, that was a plumper.
1835		Surrey Advertiser 20 Feb. 2/3: An elector, who had out run the constable, came to the poll to vote:— ‘I shall give one vote to Mr A; one vote to Mr B,’ he said; ‘And another vote to me!’ added a Sheriff’s officer, giving the atsonished voter a plumper on the shoulder.
c.1845		R. Barham ‘My Letters’ in Ingoldsby Legends (1847) 356: The devil take the rain – here goes, / I’m off – a plumper for Sir Peter!
1849		Bell’s Life in Sydney 28 Apr. 2/6: [headline] A Plumper for Nob.

4. a major lie.

1812		Salem (MA) Gaz. 26 Nov. 3/3: A Plumper.—The Gazette [...] states [...] a more barefaced falsehood never was published.
1838		M. Lemon M.P. For The Rotten Borough I iv: That’s another plumper.

5. an act of sexual intercourse.

1833

Satirist (London) 6 Jan. 429/4: ‘I gave a plumper to the reform candidate, my dear,’ answered the duke. ‘You had much better have given it to me, love,’ rejoined the duchess.

6. an unusually large version of its type.

1881

Punch 1 Oct. 155/1: Lovers of England [...] can hardly do better than help to fill that Purse, which Mr. Punch hopes will prove a ‘plumper’.