welkin

welkin \WEL-kin\, noun:

the sky; the vault of heaven.

As the elegant coach trotted through the warm night air, Rome leaned back and gazed at the welkin, trying to guess which star Home orbited about.
-- Mark S. Geston, Lords of the Starship, 1967

Down washed the rain, deep lowered the welkin; the clouds, ruddy a while ago, had now, through all the blackness, turned deadly pale, as if in terror.
-- Charlotte Brontë, Villette, 1853

Welkin comes from the Old English word welcn which meant "cloud." It was a cognate of the German word Wolke, which also meant "cloud."