holler vs roar

holler and roar both are nouns.

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

As nouns, holler and roar are synonyms defined as:

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

As verbs, roar is a hyponym of holler; that is, roar is a word with a more specific, narrower meaning than holler:

holler (noun)	roar (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	a deep prolonged loud noise
	the sound made by a lion

holler (verb)	roar (verb)
complain	laugh unrestrainedly and heartily
utter a sudden loud cry	make a loud noise, as of wind, water, or vehicles
shout out	emit long loud cries
	utter words loudly and forcefully
	make a loud noise, as of animal
	act or proceed in a riotous, turbulent, or disorderly way