A spendthrift person is reckless and wasteful with his money. If you're a spendthrift, you might find yourself in debt. However, it might be fun to have a spendthrift friend who likes to treat you to expensive lunches and lavish gifts.
Spendthrift was created by sticking two opposite words together: spend and thrift, which means “savings, wealth.” So a spendthrift spends all of his savings. Spendthrift people are the worst nightmare of retirement planners and Scrooges all over the globe. So unless you want to be called a spendthrift, think twice about your next purchase.