skyyoudaoicibaDictYouDict[sky 词源字典]
sky: [13] Our Anglo-Saxon ancestors called the sky heofon ‘heaven’. Not until the early Middle English period did heaven begin to be pushed aside by sky, a borrowing from Old Norse ský ‘cloud’. This came ultimately from an Indo- European base meaning ‘cover’, which also produced Latin obscūrus, source of English obscure [14]. (For a while English continued to use sky for ‘cloud’ as well as for ‘sky’: the medieval Scots poet William Dunbar wrote, ‘When sable all the heaven arrays with misty vapours, clouds, and skies’.)
=> obscure[sky etymology, sky origin, 英语词源]
sky (n.)youdaoicibaDictYouDict
c. 1200, "a cloud," from Old Norse sky "cloud," from Proto-Germanic *skeujam "cloud, cloud cover" (cognates: Old English sceo, Old Saxon scio "cloud, region of the clouds, sky;" Old High German scuwo, Old English scua, Old Norse skuggi "shadow;" Gothic skuggwa "mirror"), from PIE root *(s)keu- "to cover, conceal" (see hide (n.1)).

Meaning "upper regions of the air" is attested from c. 1300; replaced native heofon in this sense (see heaven). In Middle English, the word can still mean both "cloud" and "heaven," as still in the skies, originally "the clouds." Sky-high is from 1812; phrase the sky's the limit is attested from 1908. Sky-dive first recorded 1965; sky-writing is from 1922.
sky (v.)youdaoicibaDictYouDict
"to raise or throw toward the skies," 1802, from sky (n.).