Green’s Dictionary of Slang

1. the female genitals.

1720		J. Gay ‘Work for a Cooper’ in Poetical Works of John Gay (1854) 213: Her coats rose high, her master saw – I see – he cries – (then claspt her fast) The leak through which my wine has past .
1836		‘Witcomb Bay’ in Cockchafer 12: He press’d her downy billow, / And soon he stopp’d her leak.

2. (orig. US) the act of urination.

1918		implied in take a leak
1951		Kerouac On the Road (The Orig. Scroll) (2007) 180: I drank so much I had to rush out of the booth for a leak every two minutes.
1965		W. Dick Bunch of Ratbags 148: He’s just gone for a leak.
1978		R. Caron Go-Boy! 107: Hang on just a minute, will you? I gotta have a leak.
1986		F. Taylor Auf Wiedersehen Pet Two 37: He’d not even dared to stop for a leak until he’d hit the A1.
1986		C. Bowles G’DAY 5: When an Australian goes to urinate [...] he most often goes for a piss, a slash, or a leak. He hardly ever shakes hands with the wife’s best friend.
2004		T. Winton ‘Big World’ in Turning (2005) 6: We pull over for a leak.

3. (orig. US) a piece of hitherto secret information that has been revealed.

[1899		Perrysburg Jrnl 1 Sept. 6/1: For some time now a constant ‘leakage’ of these confidential documents had been noticed [...] and Dreyfus was under suspicion.
1915		R.H. Davis Frame Up 🌐 n.p.: Both your brother and Sammy [...] asked you wouldn’t use the telephone; they’re afraid of a leak.
1926		Wood & Goddard Dict. Amer. Sl.
1930		E.H. Lavine Third Degree (1931) 68: After the arrest the gang figured there must be a leak from the outside.
1945		G. Fairlie Capt. Bulldog Drummond 185: The knowledge which he had acquired [...] might be the means effectively of stopping a very dangerous leak.
1951		M. Spillane One Lonely Night 100: The leak could just as well have come out of police headquarters.
1960		C. Cooper Jr Scene (1996) 146: I’ll string out a few feelers for leaks.
1999		Guardian Media 19 July 2: A series of leaks described him as a management naif.
2016		V. McDermid Out of Bounds (2017) 81: There’s a leak somewhere in my ystrem. The media gets to hear about the cases .

4. (Aus., also leaker) an informer.

1920		F. Packard White Moll 142: Where did you get the dope you made your plays with? It was a cinch, wasn’t it, that there was a leak somewhere in our crowd.
1942		W.R. Burnett Quick Brown Fox 230: [T]here was a leak in the News-Press, and Kelly got tipped off to anything big that was coming up, just in case he missed it himself.
1976		in Woodward & Bernstein The Final Days 319: Haig had a low opinion of Hartmann [...] whom he judged a heavy drinker and a leaker.

5. (Aus.) a trick, a dodge.

1944

A. Marshall These Are My People (1957) 144: I use Eno’s Fruit Salts instead of baking powder [...] I know all the leaks.