Meaning

noun a narrow secluded valley (in the mountains)

originFrom 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.

Etymology from Wiktionary, CC BY-SA 3.0