Green’s Dictionary of Slang

plonker n.

[fig. use of SE plonk, to hit or strike with a plonking noise ]

1. anything large or substantial.

C.C. Robinson Dialect of Leeds 386: ‘A plonker’ is an article having extraordinary substance. A piece of woven material unusually thick is ‘a plonker’ .
[UK]Pudsey Almanack and Hist. Register Mar. n.p.: Sitha Bill at that young woman’s improver, isn’t it a plonker? [EDD].
B. Kirkby Lakeland Words 114: Noo that’s a plonker.
[UK] J. Wright EDD IV 550/1: That turnip’s a plonker .
[Aus]Aussie (France) 18 Jan. 3/1: [of a shell] Fritz was putting over some big stuff. Every time a plonker landed near them, one of the officers energetically fired his revolver into the air.

2. (also plonk) the penis [note plonk v. (3)].

implied in pull one’s plonker
[UK]B. Aldiss Hand-Reared Boy 54: Can I get it out? [...] Your thing. Your little plonk.
[UK]J. McDonald Dict. of Obscenity etc.
[UK]N. Barlay Crumple Zone 226: He’ll believe whatever’s in his hand that’s not his plonker.
[Scot](con. 1980s) I. Welsh Skagboys 215: I swivel my hips, watching my big placky plonker move fae side tae side.

3. (also plonk) a general term of abuse [widely popularized by the 1980s BBC TV series Only Fools and Horses].

[[US]A. Zugsmith Beat Generation 141: Listen, plink-plonkers and hipchicks].
[UK]J. Gaskell All Neat in Black Stockings 72: If she’d been my daughter in fact I’d never have let her go out with an obvious plonker like myself.
[Aus]Sun. Truth (Brisbane) 13 Sept. 36/2: Do you know what a plonker is?—It’s a chap who shares his ladyfriends with his mate [OED].
[UK]J. Sullivan ‘Cash and Curry’ Only Fools and Horses [TV script] What a plonker!
[UK] in R. Graef Living Dangerously 223: I know the guy. He’s a plonk.
[UK] C. Fowler Darkest Day (1998) 334: He was a plonker of the first order.
[UK]D. Mitchell Black Swan Green 171: You prat [...] you ponce you pillock you plonker.
[UK]Times 3 Oct. 🌐 [headline] Only a plonker would call time on sozzled bonking.

4. (Aus.) a bettor, who ‘plonks down’ their money.

[Aus]J. Byrell Lairs, Urgers & Coat-Tuggers 306: ‘We thought maybe just the old faithful plonkers we’d been used to would have a go’.

In phrases

pull one’s plonker (v.) (also pull one’s plonk)

1. to masturbate.

[UK] ‘Last Night I Lay in Bed’ in Bold (1979) 128: Last night I lay in bed and pulled my plonker.
[UK]‘J.H. Ross’ Mint (1955) 96: You should leave off pulling your plonk.

2. to fool, to mislead.

[UK]S. Bell If... 10 May in If Files (1997) 77: You’re pulling my plonker!
[UK]K. Waterhouse Soho 121: That bollox about soup spoons – were they pulling our plonkers or what?
[UK](con. 1980) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 246: All right, son. I was only pulling your plonker.