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."
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Definitions of cwm
a steep-walled semicircular basin in a mountain; may contain a lake;