derail

To derail something means to cause it to leave its intended course or path—whether literally, like a train leaving the tracks, or figuratively, like a conversation veering off-topic. You can also use it without an object: "The train derailed." The origin is quite visual: emerging in the 19th century, when trains were becoming common, "derail" specifically described a train coming off the rails.

Today, we use it much more broadly. A single question can derail a politician's carefully crafted speech. Unexpected news might derail your weekend plans, and a minor setback could derail an entire project. It implies a disruption that throws something into disarray or prevents it from continuing as planned.

It is important to note that "derail" often suggests suddenness and that it was not planned. While you might intentionally change your course, something that derails feels like an unexpected obstacle or an outside force interfering. You wouldn't typically say, "I derailed my vacation"—you would say, "I changed my vacation plans." However, you would say, "The bad weather derailed our picnic."

So, whether it is a train on the tracks or your best-laid schemes, to derail is to disrupt progress and send things off course—often unexpectedly.