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
