roar vs scream

roar and scream both are nouns.

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

As verbs, scream is a hypernym of roar; that is, scream is a word with a broader meaning than roar:

Other hypernyms of roar include call, cry, holler, hollo, shout, shout out, squall, yell.

roar (noun)	scream (noun)
a very loud utterance (like the sound of an animal)	sharp piercing cry
a deep prolonged loud noise	a joke that seems extremely funny
the sound made by a lion	a high-pitched noise resembling a human cry

roar (verb)	scream (verb)
laugh unrestrainedly and heartily	utter a sudden loud cry
make a loud noise, as of wind, water, or vehicles	utter or declare in a very loud voice
emit long loud cries	make a loud, piercing sound
utter words loudly and forcefully
make a loud noise, as of animal
act or proceed in a riotous, turbulent, or disorderly way