Kibosh!

"Well, he soon put the kibosh on THAT idea." It's a bloody odd phrase. What's a kibosh and why does the application of one instantly result in something being stopped?

Well, as is often the case with etymology, it's difficult to prove, but the generally accepted answer is that 'kibosh' derives from "cie bais" - a Gaelic phrase meaning "cap of death." This was a black skullcap worn by judges in ancient Ireland before sentencing prisoners to death.

ps. BONUS ANAL PRONUNCIATION POINT: the correct pronunciation is 'ky-bosh'. Not kee-boosh.