roar vs yell

roar and yell both are nouns.

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

As nouns, yell is a hypernym of roar; that is, yell is a word with a broader meaning than roar:

Other hypernyms of roar include call, cry, outcry, shout, vociferation.

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

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

roar (noun)	yell (noun)
a very loud utterance (like the sound of an animal)	a loud utterance; often in protest or opposition
a deep prolonged loud noise	a loud utterance of emotion (especially when inarticulate)
the sound made by a lion

roar (verb)	yell (verb)
laugh unrestrainedly and heartily	utter or declare in a very loud voice
make a loud noise, as of wind, water, or vehicles	utter a sudden loud cry
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