boo vs yell

boo and yell both are nouns.

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

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

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

boo (noun)	yell (noun)
a cry or noise made to express displeasure or contempt	a loud utterance; often in protest or opposition
	a loud utterance of emotion (especially when inarticulate)

boo (verb)	yell (verb)
show displeasure, as after a performance or speech	utter or declare in a very loud voice
	utter a sudden loud cry