bellowing vs roar

bellowing and roar both are nouns.

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

As nouns, bellowing and roar are synonyms defined as:

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

bellowing (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

bellowing (verb)	roar (verb)
	laugh unrestrainedly and heartily
	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