Welkin comes from Middle English welkin, welken ('cloud, sky'), from Old English wolcen ('cloud'), from Proto-Germanic *wolkną ('cloud'). Cognate with German Wolke ('cloud'). In current use it is a noun meaning "the sky, the vault of heaven, or the upper air". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. The historical chain includes Old English wolcen and Proto-Germanic *wolkną. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.