hollo vs shout out

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

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

As verbs, hollo and shout out are synonyms defined as:

Other synonyms of hollo include call, cry, holler, scream, shout, squall, yell.

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

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

hollo (noun)	shout out (noun)
a very loud utterance (like the sound of an animal)

hollo (verb)	shout out (verb)
utter a sudden loud cry	utter a sudden loud cry
cry hollo	utter in a very loud voice
encourage somebody by crying hollo