Brainy means having or showing great intelligence and mental ability. A brainy student might solve complex math problems quickly, remember detailed facts about ancient Egypt, or come up with creative solutions to tricky science experiments.

The word suggests someone who really uses their mind and enjoys thinking through problems and learning new things. A brainy friend might be the one who figures out the strategy to win a difficult game or explains how something works in a way that suddenly makes sense.

People sometimes use brainy to describe someone whose intelligence is obvious and impressive. You might call your teammate brainy after she devises a clever plan that wins the debate competition. Parents might describe their child as brainy when he reads complicated books or asks thoughtful questions about how the world works.

While brainy is usually a compliment, it can sometimes sound a bit informal or even slightly teasing, like calling someone a “brainiac.” But being brainy is genuinely valuable: brainy people solve problems, make discoveries, and help others understand difficult ideas. Marie Curie was brainy, and so was Benjamin Franklin. Their mental abilities changed the world.