county in the far southwest of England, from Old English Cornwalas (891) "inhabitants of Cornwall," literally "the Corn Welsh," from the original Celtic tribal name *Cornowii (Latinized as Cornovii), literally "peninsula people, the people of the horn," from Celtic kernou "horn," hence "headland," from PIE *ker- (1) "horn; head, uppermost part of the body" (see horn (n.)), in reference to the long "horn" of land on which they live. To this the Anglo-Saxons added the plural of Old English walh "stranger, foreigner," especially if Celtic (see Welsh). The Romans knew it as Cornubia; hence poetic Cornubian.
"of or pertaining to Cornwall," the county in the far southwest of England, late 14c. (as a surname), from first element of Cornwall (q.v.) + -ish. Earlier was Cornwalsche, Cornwalish (c. 1200). As a noun, the name of the ancient Celtic language of Cornwall, extinct as a spoken language since late 18c., from 1540s. Related: Cornishman.
As a noun, "the Britons," also "the Welsh language," both from Old English. The word survives in Wales, Cornwall, Walloon, walnut, and in surnames Walsh and Wallace. Borrowed in Old Church Slavonic as vlachu, and applied to the Rumanians, hence Wallachia. Among the English, Welsh was used disparagingly of inferior or substitute things (such as Welsh cricket "louse" (1590s); Welsh comb "thumb and four fingers" (1796), and compare welch (v.)). Welsh rabbit is from 1725, also perverted by folk-etymology as Welsh rarebit (1785).