Couth is a playful word meaning sophisticated, refined, or having good manners. If someone has couth, they know how to behave politely in social situations and carry themselves with grace.

Here's the interesting part: people almost never use couth by itself. Instead, you'll hear its opposite, uncouth, which means crude, awkward, or lacking manners. Someone who chews with their mouth open, interrupts constantly, or acts rudely might be called uncouth.

The word couth exists mostly as a joke or for emphasis. If your friend complains that someone at dinner was totally uncouth, you might respond playfully: “Well, I thought you were very couth!” It's like how “ruthless” is common but “ruthful” sounds funny and old-fashioned.

In modern English, couth survives mainly as a witty back-formation, proof that language doesn't always follow logical rules.