A whim is a sudden desire or decision made without much thought or planning. When you choose to do something on a whim, you're acting on impulse rather than careful consideration. You might suddenly decide to rearrange your bedroom furniture on a whim, or your dad might stop for ice cream on a whim during an ordinary drive home.

Whims are different from plans or commitments. If you've been thinking about joining the chess club for weeks, that's not a whim. But if you see a poster in the hallway and decide right then to sign up without really thinking it through, that's acting on a whim.

The word often suggests something spontaneous and somewhat unpredictable. A whimsical person follows their whims frequently, doing things that strike them as fun or interesting in the moment. Sometimes whims lead to wonderful adventures, like the time your family took a whim-driven detour and discovered an amazing hiking trail. Other times, they lead to hasty decisions you might regret, like impulsively spending all your saved allowance on something you don't really need.

Adults sometimes describe following every whim as irresponsible, meaning someone who never thinks ahead or considers consequences. But everyone enjoys an occasional whim that breaks up routine and adds a little spontaneity to life.