Wether comes from Middle English wether, from Old English weþer ('ram, castrated ram'), from Proto-Germanic *weþruz ('yearling, ram'), from Proto-Indo-European *wet- ('year'). Cognate with German Widder. In current use it is a noun meaning "a castrated male sheep". 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 weþer, Proto-Germanic *weþruz, and Proto-Indo-European *wet-. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.