Green’s Dictionary of Slang

1. a contraceptive sheath.

1934		‘J.M. Hall’ Anecdota Americana II 27: Determined to stem his virility, he finally adjusted six rain-coats on his tool and went to work.
c.1935		‘Mae West in “The Hip Flipper”’ [comic strip] Fucking with a raincoat is like peeping through a keyhole with a glass eye.
1969		in Current Sl. IV:3–4 (1970).
1972		B. Rodgers Queens’ Vernacular.
1982		P. Bailey Eng. Madam 82: All the other fellows who turned up expecting a French polishing: I made every one of them wear a rubber raincoat.
1994		N. McCall Makes Me Wanna Holler (1995) 42: Make sure you wear a raincoat when you bone them broads.
2003		McGill Reed Dict. of N.Z. Sl.
2004		R.G. Barrett Rosa Marie’s Baby (2013) [ebook] ‘I’m not wearing a raincoat’.

2. a dutch cap contraceptive.

2001

(con. late 1940s) V. Foot Sixteen Shillings And Tuppence Ha’penny 133: Blow me down – it’s the bloomin’ raincoat now (Dutch cap)!

3. (UK Und.) an Ingram Mac-10 machine pistol.

1999

Guardian G2 9 Sept. 8: The tabloids call them ‘Big Macs’; the gangsters call them ‘raincoats’.

(US) a 1950s youth hair style.

1983

N. Proffitt Gardens of Stone (1985) 112: Most of them wore pegged, button-fly Levis [...] and duck’s-ass or rain-drain haircut.

(US) water.

1953

L. Uris Battle Cry (1964) 125: Easy on the rainjuice.

1. (US Und.) a confidence trickster (or legitimate businessman) who makes extravagant promises and, if they fail to work out, extracts even more money from the victim / client.

1899–1900		C.L. Cullen Tales of the Ex-Tanks 109: He asked me if I thought I’d be able to do any rain-making [...] as to the merits of the fruit.
2004		Simon & Pelecanos ‘Middle ground’ Wire ser. 3 ep. 11 [TV script] He rain-made you. A guy says if you pay him, he can make it rain. You pay him. If and when it rains, he takes the credit. And when it doesn’t, he finds reasons for you to pay him more.

2. (US) an extremely successful member of a firm, often a lawyer, who commands high fees and is thus a lucrative asset to their employer; thus rainmaking, promoting trade.

1978		Time 10 Apr. 65: Rainmakers can come up dry: ex-Attorney General Ramsey Clark did so much free pro bono work that he lost money for his former New York firm.
2000		P. Earley Super Casino 145: ‘The way for me to rise, I decided, was by attaching myself to one of the generals in the company—someone who was clearly a rainmaker’.

an umbrella.

1821		W.T. Moncrieff Tom and Jerry II ii: Aye, put down the rain napper, Doctor, the shower is over now.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
1895		C. Crowe Aus. Sl. Dict. 64: Rain-napper, an umbrella.
1909		J. Ware Passing Eng. of the Victorian Era.

(US prison) coffee.

1935

A.J. Pollock Und. Speaks n.p.: Rainwater, coffee.