Lather is the thick, foamy bubbles that form when you mix soap or shampoo with water and rub vigorously. When you wash your hands with soap, those white, fluffy suds covering your palms are lather. The more you rub and scrub, the more lather builds up.

You create lather by trapping tiny air bubbles in soapy water. Shampoo commercials often show people with heads full of thick lather, though you don't actually need that much foam for something to get clean. Still, most people enjoy working their shampoo into a good lather because it feels satisfying and spreads the soap around evenly.

The word can also describe the foamy sweat that forms on a hard-working horse. After a long gallop on a hot day, you might see white lather on the horse's neck and flanks.

When someone works themselves into a lather over something, they're getting unnecessarily worked up or anxious, like how vigorously rubbing soap creates more and more foam. If your friend starts panicking about a quiz that's still two weeks away, you might tell them not to get into such a lather about it.