To cap something means to put a limit on it or to cover its top. When your parents cap your screen time at two hours per day, they're setting a maximum limit you can't exceed. A bottle cap covers the opening of a bottle to keep the liquid inside fresh and prevent spills.

The word also appears in sports: when you cap off a great season, you finish it in a memorable or successful way, like ending with a championship victory. In older British usage, being capped for your national team meant being selected to represent your country, because players literally received a cap to mark the honor.

You might hear someone say a story or joke caps all the others, meaning it's the best one or the perfect ending to a series. When mountain climbers talk about a snow cap, they mean the white snow covering a mountain's peak.

The word has taken on a new meaning in modern slang, where “no cap” means “no lie” or “I'm being truthful,” though this usage is quite informal and constantly evolving.