It's always seemed odd to us that in the Lake District the hills are known as "fells". How could they be fells when they went up? But there was clearly a pattern of local names for things as other words came up again and again. Like "gill" or "ghyll" for a narrow valley or stream, "force" for a waterfall, or "pike" for a peak.Cumbrian toponymy1 and all became clear. It turns out that all of these words, and more besides, are from Old Norse. The Norse appear to have arrived in Cumbria in about 925 AD and were originally from Norway. They left a wealth of words behind them in the Lake District derived from Old Norse including:
There were other influences too including Iron Age Celts (who left us with "crag"), Old English ("mere"), and Anglo-Norman and Middle English ("great"), but we'll leave you to read the whole Wikipedia article if you want to know more.
Words from the past also crop up elsewhere in Cumbria. The Herdwick sheep for example takes its name from the Old Norse herdvyck, a sheep pasture, and a mole is still referred to locally as a mowdy or mowdywarp from the Early Modern English mouldywarp for a mole2.