roar vs vroom

roar and vroom both are nouns.

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

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

Other hyponyms of roar include bawl, yawp, thunder.

roar (noun)	vroom (noun)
a very loud utterance (like the sound of an animal)	the roaring sound made by a motor that is running at high speed
a deep prolonged loud noise
the sound made by a lion

roar (verb)	vroom (verb)
laugh unrestrainedly and heartily	make a loud, roaring sound, as of a car engine, while moving
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