halloo vs yell

halloo and yell both are nouns.

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

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

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

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

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

halloo (noun)	yell (noun)
a shout to attract attention	a loud utterance; often in protest or opposition
	a loud utterance of emotion (especially when inarticulate)

halloo (verb)	yell (verb)
shout `halloo', as when greeting someone or attracting attention	utter or declare in a very loud voice
urge on with shouts	utter a sudden loud cry