Ace means the best at something or to perform perfectly. When someone aces a test, they get every question right. A pilot who shoots down five enemy planes becomes a “flying ace.” In tennis, an ace is a serve so perfect the opponent can't even touch it.

The word comes from playing cards, where the ace is often the highest or most powerful card. In many card games, drawing an ace gives you a strong advantage. This meaning carried over into everyday language: calling someone an ace means they're exceptionally skilled at what they do, like an ace reporter who always gets the story or an ace mechanic who can fix any engine.

You might say your friend is an ace at math when she solves problems faster than anyone else. Or you could announce, “I aced it!” after nailing a piano recital you'd practiced for weeks. The word captures that feeling of excellence, when everything comes together perfectly and you perform at your very best.