To imperil something means to put it in danger or at risk of being harmed or destroyed. When you imperil something, you're doing something that could cause serious damage or loss, even if you don't intend to.

A hiker who wanders off the trail in a snowstorm imperils their own safety. A student who waits until the last minute to start a major project imperils their grade. When a sea captain ignores storm warnings, they imperil the ship and crew.

You'll often see this word when someone is warning about risks: “Cutting corners on safety procedures could imperil workers” or “Forgetting to save your work imperils hours of effort.”

Notice that imperil suggests serious consequences, not minor problems. You wouldn't say someone imperiled their afternoon by forgetting a snack. But you would say a firefighter imperiled their life to save others, or that lying to a friend imperils the friendship itself.