landslide (n.)

Old English lond, land, "ground, soil," also "definite portion of the earth's surface, home region of a person or a people, territory marked by political boundaries," from Proto-Germanic *landja- (source also of Old Norse, Old Frisian Dutch, Gothic land, German Land), perhaps from PIE *lendh- (2) "land, open land, heath" (source also of Old Irish land, Middle Welsh llan "an open space," Welsh llan "enclosure, church," Breton lann "heath," source of French lande; Old Church Slavonic ledina "waste land, heath," Czech lada "fallow land"). But Boutkan finds no IE etymology and suspects a substratum word in Germanic,

Etymological evidence and Gothic use indicates the original Germanic sense was "a definite portion of the earth's surface owned by an individual or home of a nation." The meaning was early extended to "solid surface of the earth," a sense which once had belonged to the ancestor of Modern English earth (n.). Original senses of land in English now tend to go with country. To take the lay of the land is a nautical expression. In the American English exclamation land's sakes (1846) land is a euphemism for Lord.

1560s, "act, fact, or manner of sliding," from slide (v.). As a smooth inclined surface down which something can be slid, from 1680s.

The playground slide is by 1900, short for sliding board (1899). The meaning "collapse of a hillside, landslide" is attested from 1660s. As a working part of a musical instrument from 1800 (as in slide-trombone, 1891, as opposed to one with keys). The meaning "rapid downturn" is from 1884.

The meaning "picture prepared for use with a projector" is from 1819 (in reference to magic lanterns); earlier it was called a slider (1793). The base-running sense in baseball is attested by 1886. Slide-guitar is from 1968; the effect is attained by sliding an object (beer bottle neck, etc.) along the strings.

1670s, from land (n.) + slip (n.). Compare landslide.