1856, Amer.Eng., from land (n.) + slide. Earlier was landslip (1679), still preferred in Britain. In the political sense, landslide "lopsided electoral victory" is attested from 1888.
The rapid downward sliding of a mass of earth and rock. Landslides usually move over a confined area. Many kinds of events can trigger a landslide, such as the oversteepening of slopes by erosion associated with rivers, glaciers, or ocean waves; heavy snowmelt which saturates soil and rock; or earthquakes that lead to the failure of weak slopes.