Other forms: leaked, leaks, leaking
A leak is a hole letting out something that should have stayed in — water from a pipe, gas from a valve, air from a tyre. It is also the escaping itself: the puddle under the boiler, the brown ring spreading across the ceiling.
The verb covers both sides of it: the roof leaks, and the roof leaks water. The famous second sense is about information — a leak is a secret handed quietly to a journalist, and the person inside who handed it over leaked it. That gives you leaked documents, a leaked email, and a leak inquiry to find the culprit. Notice the pairing with OUT: news leaks out, and somebody leaks it out. Take a leak is ordinary spoken English for going to the toilet, so keep it well away from your writing.
1nouncrackA hole or crack that lets liquid or gas escape.
“There is a leak in the radiator pipe under the stairs.”
2nounleakSecret information passed to the press without permission.
“The leak came from somebody inside the department.”
3verbliquidTo let liquid or gas escape through a hole.
“The old kettle leaks whenever you fill it to the top.”
4verbgiveTo give secret information to the press.
“Someone leaked the report to a newspaper a week before publication.”
Too few real examples of this word to estimate which sense is commonest.
Leak goes back to Middle English leken, to let water in or out, with Old English, Middle Dutch leken and Old Norse leka all in the same family. Behind them sits Proto-Germanic *lekaną, to leak or drain, from a Proto-Indo-European root with the same job. Water came first by a very long way; the secrets are a modern borrowing of the picture.
Proto-Indo-European
*leg- — to leak
Proto-Germanic
*lekaną — to leak, drain
Old Norse
leka — to leak, drip
Middle Dutch
leken — to leak, drip
Old English
*lecan — to leak
Middle English
leken — to let water in or out
English, today
leak
From Middle English leken (“to let water in or out”), from Old English lecan (“to leak”), Middle Dutch leken (“to leak, drip”) or Old Norse leka (“to leak, drip”); all from Proto-Germanic lekaną (“to leak, drain”), from Proto-Indo-European leg- (“to leak”). Cognate with Dutch lekken (“to leak”), German lechen, lecken (“to leak”), Danish lække (“to leak”), Swedish läcka (“to leak”), Norwegian Bokmål lekke (“to leak”), Faroese, Icelandic and Norwegian Nynorsk leka (“to leak”). Related also to Old English leċċan (“to water, wet”), Albanian lag, lak (“to damp, make wet”). See also leach, lake. divulgation, disclosure of information Compare typologically изтичане, przeciek, уте́чка (akin to течь).
Etymology from Wiktionary, CC BY-SA