bellow vs yell

bellow and yell both are nouns.

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

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

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

bellow (noun)	yell (noun)
a very loud utterance (like the sound of an animal)	a loud utterance; often in protest or opposition
	a loud utterance of emotion (especially when inarticulate)

bellow (verb)	yell (verb)
shout loudly and without restraint	utter or declare in a very loud voice
make a loud noise, as of animal	utter a sudden loud cry