in Germanic cosmology, "the abode of the human race, the world inhabited by men" (opposed to Asgard, the abode of the gods), by 1770, from Old Norse miðgarðr, from mið "mid" (from PIE root *medhyo- "middle") + Proto-Germanic *gardoz "enclosure, tract" (from PIE root *gher- (1) "to grasp, enclose;" compare yard (n.1)). The Old English cognate was middangeard, which later was folk-etymologized as Middle Earth.
"the earth regarded as placed midway between heaven and hell or the abode of the gods and the underworld," late 13c., from middle (adj.) + earth. Altered from earlier middel-erd (late 12c.), midden-erd, itself an alteration (by association with Middle English eard "dwelling") of Old English middangeard (see Midgard).
Old English woruld, worold "human existence, the affairs of life," also "a long period of time," also "the human race, mankind, humanity," a word peculiar to Germanic languages (cognates: Old Saxon werold, Old Frisian warld, Dutch wereld, Old Norse verold, Old High German weralt, German Welt), with a literal sense of "age of man," from Proto-Germanic *weraldi-, a compound of *wer "man" (Old English wer, still in werewolf; see virile) + *ald "age" (from PIE root *al- (2) "to grow, nourish").
Originally "life on earth, this world (as opposed to the afterlife)," sense extended to "the known world," then to "the physical world in the broadest sense, the universe" (c. 1200). In Old English gospels, the commonest word for "the physical world," was Middangeard (Old Norse Midgard), literally "the middle enclosure" (see yard (n.1)), which is rooted in Germanic cosmology. Greek kosmos in its ecclesiastical sense of "world of people" sometimes was rendered in Gothic as manaseþs, literally "seed of man." The usual Old Norse word was heimr, literally "abode" (see home). Words for "world" in some other Indo-European languages derive from the root for "bottom, foundation" (such as Irish domun, Old Church Slavonic duno, related to English deep); the Lithuanian word is pasaulis, from pa- "under" + saulė "sun."
Original sense in world without end, translating Latin saecula saeculorum, and in worldly. Latin saeculum can mean both "age" and "world," as can Greek aiōn. Meaning "a great quantity or number" is from 1580s. Out of this world "surpassing, marvelous" is from 1928; earlier it meant "dead." World Cup is by 1951; U.S. baseball World Series is by 1893 (originally often World's Series). World power in the geopolitical sense first recorded 1900. World-class is attested from 1950, originally of Olympic athletes.