From Middle English Walsch, Welische, from Old English wīelisċ ("Briton; Roman; Celt"), from Proto-West Germanic *walhisk, from Proto-Germanic *walhiskaz ("Celt; later Roman"), from *walhaz (compare Old English wealh), from the name of the Gaulish tribe, the Volcae (recorded only in Latin contexts).
This word was borrowed from Germanic into Slavic (compare Old Church Slavonic Влахъ ("Vlachs, Romanians"), Byzantine Greek Βλάχος).