Old English eorþe "ground, soil, dirt, dry land; country, district," also used (along with middangeard) for "the (material) world, the abode of man" (as opposed to the heavens or the underworld), from Proto-Germanic *ertho (source also of Old Frisian erthe "earth," Old Saxon ertha, Old Norse jörð, Middle Dutch eerde, Dutch aarde, Old High German erda, German Erde, Gothic airþa), perhaps from an extended form of PIE root *er- (2) "earth, ground."
The earth considered as a planet was so called from c. 1400. Use in old chemistry is from 1728. Earth-mover "large digging machine" is from 1940.
early 14c., "a trembling in fear," from quake (v.). Rare except in combinations, and now usually as a shortening of earthquake, in which use it is attested from 1640s. Old English had the verbal noun cwacung "shaking, trembling." Also compare Middle English quavinge of erþe "an earthquake" (14c.), earthquave (n.), early 15c.
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Definitions of earthquake from WordNet
shaking and vibration at the surface of the earth resulting from underground movement along a fault plane or from volcanic activity;