earth (n.) Look up earth at Dictionary.com
Old English eorþe "ground, soil, dry land," also used (along with middangeard) for "the (material) world" (as opposed to the heavens or the underworld), from Proto-Germanic *ertho (cognates: Old Frisian erthe "earth," Old Saxon ertha, Old Norse jörð, Middle Dutch eerde, Dutch aarde, Old High German erda, German Erde, Gothic airþa), from PIE root *er- (2) "earth, ground" (cognates: Middle Irish -ert "earth"). The earth considered as a planet was so called from c.1400.