Glen
late Middle English: from Scottish Gaelic and Irish gleann (earlier glenn ).
wiktionary
From Middle English glen, borrowed from Irish gleann and Scottish Gaelic gleann, Old and Middle Irish glend, glenn(“ mountain valley”), from Proto-Celtic *glendos(“valley”), hypothetically from Proto-Indo-European *glend-(“ shore”) but the word may have been borrowed from a non-Indo-European substrate language. Compare Manx glion, Welsh glyn. Doublet of glyn.
etymonline
glen (n.)
"narrow valley," late 15c., from Scottish, from Gaelic gleann "mountain valley" (cognate with Old Irish glenn, Welsh glyn). Common in place names such as Glenlivet (1822), a kind of whiskey, named for the place it was first made (literally "the glen of the Livet," a tributary of the Avon); and Glengarry (1841) a kind of men's cap, of Highland origin, named for a valley in Inverness-shire.
