Old English wald (Anglian), weald (West Saxon, Kentish) "forest, wooded upland," from Proto-Germanic *walthuz (source also of Old Saxon and Old Frisian wald, Middle Dutch woude, wold, Dutch woud, Middle Low German walde, Old High German wald, German Wald "forest," Swedish vall "pasture," Old Norse völlr "soil, field, meadow"), from PIE root *welt- "woods; wild." The sense development from "forested upland" to "rolling open country" (c. 1200) perhaps is from Scandinavian influence, or a testimony to the historical deforestation of Britain. Not current since mid-16c.; survives mainly in place names (such as Cotswold).
<a href="https://www.etymonline.com/word/Cotswold">Etymology of Cotswold by etymonline</a>
Harper, D. (n.d.). Etymology of Cotswold. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Cotswold