To depreciate means to decrease in value over time. When you buy a new bicycle, it depreciates the moment you ride it home: it's now a used bike worth less than what you paid. Cars depreciate quickly too. A brand new car loses thousands of dollars in value during its first year, even if the owner takes perfect care of it.

Most physical things depreciate because they get older, wear out, or become outdated. A computer depreciates as newer, faster models come out. Furniture depreciates as it gets scratched and worn. Even buildings can depreciate if they're not maintained properly.

Some things work the opposite way, though. Rare collectibles, fine art, or antiques might appreciate (increase in value) over time instead of depreciating. A vintage baseball card could be worth far more now than when it was new.

The word can also mean to criticize or belittle something, making it seem less valuable than it is. If you depreciate your friend's accomplishment by saying, “That was easy, anyone could do it,” you're unfairly reducing its importance. This usage is less common, but it means essentially the same thing: making something worth less, whether in dollars or in respect.