valley vs glen

valley and glen both are nouns.

Word	Noun	Adjective	Verb	Adverb
valley	Yes	No	No	No
glen	Yes	No	No	No

As nouns, glen is a hyponym of valley; that is, glen is a word with a more specific, narrower meaning than valley:

valley: a long depression in the surface of the land that usually contains a river
glen: a narrow secluded valley (in the mountains)

Other hyponyms of valley include dale, gully, holler, hollow, nullah, ravine, rift valley.

valley (noun)	glen (noun)
a long depression in the surface of the land that usually contains a river	a narrow secluded valley (in the mountains)