landslide

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The downward sliding of a relatively dry mass of earth and rock.
• noun The mass that slides.
• noun An overwhelming majority of votes for a political party or candidate.
• noun An election that sweeps a party or candidate into office.
• noun A great victory.

from The Century Dictionary.

• noun A falling or sliding down of a mass of soil, detritus, or rock on a mountain-side.

from the GNU version of the Collaborative International Dictionary of English.

• noun The slipping down of a mass of land from a mountain, hill, etc.
• noun The land which slips down.
• noun An election victory in which the winning candidate receives a substantial majority of the votes, usually meaning at least ten per cent more than any opposing candidate.
• noun Any overwhelming victory.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A natural disaster that involves the breakup and downhill flow of rock, mud, water and anything caught in the path.
• noun A vote won by a wide or overwhelming majority.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an overwhelming electoral victory
• noun a slide of a large mass of dirt and rock down a mountain or cliff