Where Do Idioms Actually Come From?

"It's raining cats and dogs" makes zero literal sense. So why do we say it?

"Break a leg." "Spill the beans." "Bite the bullet." None of these mean what the words literally say — and yet everyone who speaks English just... understands them. These are called idioms, and most of them have a surprisingly specific backstory.

What is an idiom, exactly?

An idiom is a phrase whose meaning isn't obvious from the individual words — you have to already know what it means as a whole. If someone unfamiliar with English heard "it's raining cats and dogs," they might reasonably picture animals falling from the sky. Idioms only work because a whole community of speakers has agreed, over time, on what the phrase really means.

A few real origin stories

• "Bite the bullet" likely comes from old battlefield surgery, before anesthesia existed — wounded soldiers were sometimes given a bullet to bite down on to cope with the pain.
• "Spill the beans" may come from an ancient voting method where people cast votes using beans in a jar — knocking it over early would reveal the results before they were supposed to be known.
• "Break a leg" is a good luck phrase actors say to each other before a show, based on an old superstition that saying "good luck" directly would jinx the performance.

Not every idiom's origin is perfectly confirmed — language historians sometimes disagree — but the stories behind them are almost always more interesting than the phrase itself.

Why languages are full of them

Idioms build up naturally in any language spoken long enough by enough people. They're a kind of shared shortcut — a whole idea packed into a few familiar words, understood instantly by anyone in on the shared history.

Try it yourself

Pick an idiom you use all the time — "spill the tea," "piece of cake," "cost an arm and a leg" — and try to guess its origin before looking it up. See how close you get.