(n.) a large county in the far southwest of England
An evergreen HH fact: the ‘–wall’ in Cornwall and the ‘wal–’ in walnut are the same. Both derive from an Old English word, wealh, that essentially meant ‘stranger’, ‘foreigner’, or more specifically, ‘Celt’.
In the case of Cornwall, Old English wealh has been attached to an old Celtic word thought to be something along the lines of Cornowii—the name of the ancient people who once inhabited the region we now know as Cornwall.
That ancient tribal name probably in turn comes from an even more ancient word root meaning ‘horn’—likely a figurative reference to the peninsula or horn of land in the far southwest of England that was inhabited by the ancient Cornish people.
As for walnut, its story is a little more straightforward: in this instance, Old English wealh refers to the fact that walnuts are not native to Britain, and had to be imported from the continent. Quite simply, walnuts are foreign nuts.