I used to teach English to international students, and the idioms were always the hardest part. You can explain grammar with rules. You can explain vocabulary with translations. But how do you explain "it's raining cats and dogs" to someone who has never heard it before? "You see, when it rains very heavily, English speakers say that small domesticated animals are falling from the sky. No, not literally. Yes, I know that doesn't make sense. Yes, you still have to learn it." The look of bewildered horror on my students' faces was always the same. So let me tell you some of the best origin stories โ though I should warn you, a lot of idiom origins are disputed, and some of the most popular explanations are completely wrong.
"Raining Cats and Dogs" โ A Grim Urban Reality
The most widely accepted theory about this phrase is that it comes from 17th- and 18th-century London, where heavy rainstorms would flood the streets. The drainage systems of the time were, to put it mildly, not great. Dead animals โ including stray cats and dogs โ would accumulate in gutters and drainage ditches, and when a really heavy storm hit, the rushing water would sweep them down the streets. People walking outside during or after such a storm would see dead cats and dogs rushing past in the floodwater. That's the grim, practical origin: heavy rain literally made it look like cats and dogs had been falling from the sky.
An alternative theory โ less plausible but more poetic โ connects the phrase to Norse mythology, where cats were associated with rain and dogs with wind. The god Odin was depicted with wolves and dogs (symbols of wind), while witches (who rode on brooms during storms) were associated with cats. This theory is probably too neat โ the Norse influence on English idioms from the 17th century is pretty indirect โ but it's a nice story.
"Kick the Bucket" โ Slaughterhouse Origins
This idiom means "to die," and its origin is genuinely unsettling. The leading theory is that it comes from the practice of slaughtering pigs. In traditional slaughterhouses, a pig would be hoisted up by its hind legs from a wooden beam. That beam was sometimes called a "bucket" (from the French buquet, meaning a balance or yoke). As the animal died, its legs would spasm and "kick the bucket." The phrase then extended metaphorically to human death. A competing theory โ somewhat less macabre โ suggests that people who hanged themselves would stand on a bucket, kick it away, and... well, you get the picture. Either way, the idiom has a pretty dark history that most people who casually say "he kicked the bucket" have no idea about.
"Let the Cat Out of the Bag" โ Medieval Fraud
This one's my favorite because it involves an actual historical con. In medieval and early modern markets, piglets were a valuable commodity, often sold in sacks (bags) at the market. Unscrupulous sellers would sometimes substitute a cat for a piglet โ a cat in a sack feels roughly the same weight and size as a young pig, especially to a hurried buyer who doesn't check. If the buyer opened the sack before getting home, the cat would escape, literally "letting the cat out of the bag" and revealing the fraud. The related phrase "don't buy a pig in a poke" (meaning don't buy something without inspecting it first) comes from the same scam โ a "poke" being an old word for a sack.
"Butter Someone Up" โ An Ancient Indian Custom
This idiom meaning "to flatter someone" has a surprisingly ancient and specific origin. In ancient India, people would throw balls of clarified butter (ghee) at statues of the gods as an act of devotion, hoping the gods would look favorably upon them and grant their prayers. The practice of "buttering" deities to gain their favor was known across the ancient world โ the Tibetans had a similar custom of creating butter sculptures as offerings. From religious butter-offering to metaphorical flattery is a pretty direct conceptual leap: you're coating someone in metaphorical butter, hoping the smoothness and richness will translate into favorable treatment.
"Bite the Bullet" โ War Surgery
This idiom โ meaning to endure a painful or unpleasant situation with courage โ has a very specific origin in battlefield medicine. In the days before anesthesia (which started being widely used in the 1840s), soldiers undergoing surgery โ amputation, usually โ were literally given a bullet to bite down on. The soft lead of the bullet gave their teeth something to grip without breaking, and it also kept them from biting their own tongues during the pain. The phrase "bite the bullet" thus refers to steeling yourself for something terrible that you just have to get through.
A Warning About Folk Etymology
I should add a note of caution here: many popular idiom origin stories are folk etymology โ stories that people want to be true because they're colorful and satisfying, but that lack historical evidence. The "cats and dogs" Norse mythology explanation might be an example. The "bite the bullet" origin, while widely repeated, has some historians arguing that lead bullets would have been too hard and toxic to safely bite, and that soldiers might have bitten on leather straps instead. The pig-slaughtering origin of "kick the bucket" is plausible but not definitively proven.
This uncertainty is actually part of what makes idioms so interesting. They're oral traditions โ passed down in speech long before they were written down โ and their origins are often irrecoverably lost to history. What we have is a collection of the best guesses, each one a little story about how our ancestors lived, worked, cheated each other in marketplaces, and endured surgery without painkillers. The idioms themselves are fossils of forgotten experiences. Every time you say "it's raining cats and dogs," you're speaking a sentence whose origins trace back to London streets filled with floodwater and animal carcasses โ whether you know it or not.