valley vs holler

valley and holler both are nouns.

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

As nouns, holler is a hyponym of valley; that is, holler 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
holler: a small valley between mountains

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

valley (noun)	holler (noun)
a long depression in the surface of the land that usually contains a river	a very loud utterance (like the sound of an animal)
	a small valley between mountains