Welsh

Welsh (Cymraeg) is a language spoken in Wales. It is a member of the Celtic family of languages, and is said to be spoken by over a fifth of the population of Wales. (The most commonly spoken language is English.)

One of the curiosities of etymology is that Welsh, which is what the English language calls the Celts who preceded the Anglo-Saxons in the occupation of the British Isles, is derived from an Old English word meaning 'foreigner'. (The OED says that it is derived from "O[ld] E[nglish] wealh, O[ld] H[igh] G[erman] walah 'Welshman', i.e. Celtic or Roman foreigner".) In their own language, the Welsh call themselves cymry, from which we get our word Cambrian used to mean 'Welsh' in formal contexts, particularly of geography and geology, where Cambrian means a group of very old rocks originally identified in Wales. Now, indeed, precambrian is used to describe "the earliest division of geological time, from the formation of the earth, believed to have been about 4,600 million years ago, to the beginning of the Cambrian period and the Phanerozoic eon, about 542 million years ago" (OED).