Meaning

noun the apparent surface of the imaginary sphere on which celestial bodies appear to be projected

originInherited from Middle English welkne (“weather; heavens; (earlier) cloud”), from Old English wolcnu (“sky, heavens”), plural form of wolcn (“cloud”), from Proto-West Germanic *wolkn (“cloud”), from Proto-Germanic *wulkną (“cloud”), possibly from Proto-Indo-European *wĺ̥ɡ-no-m, from *welg- (“damp; wet”). Cognate with Dutch wolk (“cloud”), German Wolke (“cloud”).

Etymology from Wiktionary, CC BY-SA 3.0