Valley, glen. Written Glen, Glan — the same Irish word, gleann, in the spellings English gave it.
Gleann is a valley, and Glen- names are as common as the valleys — Glendalough, the glen of the two lakes; Glenveagh; the nine Glens of Antrim. English borrowed the word itself, so that glen is now an English word for exactly what it means in Irish.
Source: P. W. Joyce, The Origin and History of Irish Names of Places (1869–1913) · Logainm ↗
Valley, glen: it is the Irish gleann. Gleann is a valley, and Glen- names are as common as the valleys — Glendalough, the glen of the two lakes; Glenveagh; the nine Glens of Antrim. English borrowed the word itself, so that glen is now an English word for exactly what it means in Irish.
gleann. English spellings of the same word include Glen, Glan, because the names were written down by ear.