Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
GLEN
As described in historical dictionaries
Patronymica Britannica (1860)
1" GLEN. A common syllable in Celtic names of places, as Glendinning, Glendor, Glencaglis, Glenister, Glenfield, Glcnham, Glenuio, Glenuj', and Glenton.
Surname type: Location or geographical feature
Origin: Celtic
Region of origin: British Isles
Country of origin: Scotland
Religion of origin: Christian
Language of origin: Gaelic