also combe, "deep hollow or valley, especially on flank of a hill," mainly surviving in place names, from Old English cumb, probably a British word, from Celtic base *kumbos (compare Welsh cwm in same sense). Cambridge Dictionary of English Place-Names says, "This is usually taken to be a Celtic loan ... but there was also OE cumb 'vessel, cup, bowl,'" which was "probably used in a transferred topographical sense reinforced in western districts by cwm."
<a href="https://www.etymonline.com/word/cwm">Etymology of cwm by etymonline</a>
Harper, D. (n.d.). Etymology of cwm. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/cwm