A more thorough explanation:

Definition: One who spends money recklessly and wastefully.

Example: John is a spendthrift who always buys expensive clothes and gadgets, even though he can't afford them.

Explanation: The example illustrates the definition of spendthrift by showing a person who spends money without thinking about the consequences. John's behavior is reckless and wasteful because he is spending money he doesn't have on things he doesn't need.