Source : Webster's Revised Unabridged Dictionary (1913)

Landslip \Land"slip`\, Landslide \Land"slide`\, n.
   1. The slipping down of a mass of land from a mountain, hill,
      etc.

   2. The land which slips down.

Source : WordNet®

landslide
     n 1: an overwhelming electoral victory; "Roosevelt defeated
          Hoover in a landslide"
     2: a slide of a large mass of dirt and rock down a mountain or
        cliff [syn: {landslip}]