A spendthrift is someone who spends money carelessly and wastefully, burning through it without thinking about the future or whether they really need what they're buying. The word combines “spend” with an old word “thrift,” which means careful management of money, so a spendthrift is literally someone who spends their thrift away.

Imagine a kid who receives birthday money and immediately buys expensive snacks, cheap toys that break the next day, and random things they don't actually want, then complains a week later about being broke. That's spendthrift behavior. A spendthrift buys on impulse, chases every new thing that catches their eye, and rarely saves for something that actually matters.

The opposite of a spendthrift is someone thrifty, a person who spends money thoughtfully and saves for important goals. While a thrifty person might research the best value and wait for a good deal, a spendthrift grabs whatever looks appealing in the moment.

The word often describes people with serious money problems. Learning about money and how it works when you're young can help you avoid becoming a spendthrift later, when the stakes are much higher than birthday cash.