Etymology 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.
1
A secluded and narrow valley, especially one with a river running through it; a depression between hills; a dale.
What riches too, of gold and jewels, might not be hidden among those forest-shrouded glens and peaks? And beyond, and beyond again, ever new islands, new continents perhaps, an inexhaustible wealth of yet undiscovered worlds.1871, Charles Kingsley, “Down the Islands”, in At Last: A Christmas in the West Indies. […], volume I, London; New York, N.Y.: Macmillan and Co., →OCLC, page 41:
In the glens of the hills about Strathsporran are many noble and nimble stags. But I have never set foot in my house there, for it is carpeted throughout with the tartan of my clan.1911 October 26, Max Beerbohm, Zuleika Dobson, or, An Oxford Love Story, 1st American edition, New York, N.Y.: John Lane Company, published 1912, →OCLC: