A madman is someone who acts in wild, reckless, or irrational ways, often without concern for danger or consequences. If your friend rides their bike down a steep hill with no hands while standing on the seat, you might yell, “You're a madman!” You don't literally mean they're insane: you mean they're taking extreme risks that most people wouldn't dare attempt.

The word has also been used to describe someone with a serious mental illness, but that use can be hurtful or unfair. In everyday conversation, people usually use it more playfully or dramatically. When a coach pushes a team to practice in pouring rain, players might joke that he's a madman. When a scientist works through the night for weeks on a breakthrough experiment, colleagues might call him a madman with grudging admiration.

You'll often hear madman used to describe someone showing fierce determination or wild energy. A basketball player driving through three defenders for a layup plays like a madman. An inventor building strange contraptions in their garage might be called a madman, especially if their ideas seem outlandish but brilliant.