An Etymological Dictionary of the German Language/Annotated/Wolke
Wolke, feminine, ‘cloud,’ from the equivalent Middle High German wolken, Old High German wolchan, masculine; also in Middle High German (Alemannian, Middle German) wolke, Old High German wolcha, feminine, ‘cloud.’ Corresponding to Old Saxon wolcan, neuter, Dutch wolk, Anglo-Saxon wolcen, ‘cloud’ (to which English welkin is allied). Under welk a pre-Teutonic root welg, ‘moist,’ is assumed, with which the term wolkôn (wolken-), neuter, ‘cloud’ (literally ‘the moist thing’), peculiar to West Teutonic, is connected.