bellow vs roar

bellow and roar both are nouns.

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

As nouns, bellow and roar are synonyms defined as:

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

As verbs, bellow and roar are synonyms defined as:

bellow (noun)	roar (noun)
a very loud utterance (like the sound of an animal)	a very loud utterance (like the sound of an animal)
	a deep prolonged loud noise
	the sound made by a lion

bellow (verb)	roar (verb)
shout loudly and without restraint	laugh unrestrainedly and heartily
make a loud noise, as of animal	make a loud noise, as of wind, water, or vehicles
	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