holler out vs shout

holler out is not a noun while shout is a noun.

Word	Noun	Adjective	Verb	Adverb
holler out	No	No	Yes	No
shout	Yes	No	Yes	No

As verbs, shout is a hypernym of holler out; that is, shout is a word with a broader meaning than holler out:

holler out: shout out
shout: utter in a loud voice; talk in a loud voice (usually denoting characteristic manner of speaking)

holler out (noun)	shout (noun)
	a loud utterance; often in protest or opposition

holler out (verb)	shout (verb)
shout out	utter in a loud voice; talk in a loud voice (usually denoting characteristic manner of speaking)
	utter a sudden loud cry
	utter aloud; often with surprise, horror, or joy
	use foul or abusive language towards