We might assume that the common names we have for things are accurate descriptions of them, but that’s not always true.

Birthday Party

You can only have one birth day—the day you were born. After that, every time you celebrate your birthday you’re really throwing an anniversary party.

Killer Whale

They’re neither killers nor whales. They were once thought to be man-eaters. The 1973 U.S. Navy diving manual even warns that killer whales “will attack human beings at every opportunity.” But they were wrong—there are very few documented cases of attacks on human. (Seals and penguins are a different story.) And they’re members of the dolphin, not the whale, family.

Wild Rice

It’s neither wild, nor rice. Officially known as Zizania aquatica, this once-wild grass seed is now cultivated by farmers worldwide.

Radiator

Whether it’s in your home or in your car, radiators work by convecting heat—moving it via a liquid or gas, not by radiating. The radiator in your home heats the air currents around it until enough is heated to make the room feel warm. The one in your car transfers heat from the engine to water, which passes it to the atmosphere. The “radiators” radiate a little, but not much.

Poison Ivy

It’s not a poison, it’s an allergen. Poisons are harmful to everybody; allergens only affect some people. Poison ivy can cause severe itching and swelling, but many people aren’t even affected by it. It’s not ivy, either—it’s a member of the sumac family.

Ringworm

This infection makes “ring-like” marks on skin—but there are no worms involved. It’s caused by a fungus.

Heavy Cream

When milk producers say “heavy,” they actually mean “full of fat,” and the fat is the lightest part of the milk. That means that “heavy cream,” which contains as much as 30% milk fat, is actually a lot lighter than skim milk, which contains only trace amounts of fat.