shout vs holler out

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

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

As verbs, holler out is a hyponym of shout; that is, holler out is a word with a more specific, narrower meaning than shout:

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

Other hyponyms of shout include scream, yell, holler, roar, thunder, bawl, bellow.

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

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