yowl vs holler

yowl and holler both are nouns.

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

As nouns, yowl and holler are synonyms defined as:

Other synonyms of yowl include bellow, bellowing, holla, hollering, hollo, holloa, roar, roaring.

yowl (noun)	holler (noun)
a very loud utterance (like the sound of an animal)	a very loud utterance (like the sound of an animal)
	a small valley between mountains