An Etymological Dictionary of the German Language/welsch
welsch, adj., ‘foreign, outlandish (espec. Italian or French),’ from MidHG. węlsch (węlhisch, walhisch), ‘Romance, French, Italian,’ OHG. walhisc, ‘Romance’; a derivative of MidHG. Walch, OHG. Walh, ‘one of the Latin race.’ The corresponding AS. Wealh was applied to the ‘Kelt,’ and this is the lit. meaning of the word (comp. the Keltic tribal name Volcae, on which Teut. Walho- is based; it was applied to the Latin race when they occupied Gaul, which had been formerly inherited by the Kelts. Comp. further Walnuß and the E. local names Wales (AS. Wălas) and Cornwall.