earth (n.)
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.