Lengthy means taking a long time or extending over a considerable distance. A lengthy book might have 800 pages, a lengthy movie might run for three hours, and a lengthy explanation goes on and on when a shorter one would do.

The word suggests something that feels too long or unnecessarily extended. When your teacher assigns a lengthy homework assignment, you know you'll be working on it for a while. A lengthy delay at the airport means hours of waiting, not just a few minutes.

You might hear someone complain about a lengthy process, like getting a passport, which requires filling out forms, gathering documents, waiting for approval, and more waiting. The word captures that sense of duration stretching out. Compare this to something simply being “long”: a long rope is just a measurement, but a lengthy meeting suggests time dragging on.

Writers sometimes choose “lengthy” when they want to emphasize that the length matters or affects the experience. A lengthy explanation might lose your attention halfway through, while a clear, brief one gets straight to the point.