"narrow valley," 1489, from Scottish, from Gaelic gleann "mountain valley" (cf. Welsh glyn). Common in place names, cf. Glenlivet (1822), a kind of whiskey, named for the place it was first made (lit. "the glen of the Livet," a tributary of the Avon); and Glengarry (1841) a kind of man's cap, of Highland origin.
[glen] 
