pipe up vs hollo

pipe up is not a noun while hollo is a noun.

Word	Noun	Adjective	Verb	Adverb
pipe up	No	No	Yes	No
hollo	Yes	No	Yes	No

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

Other hypernyms of pipe up include call, cry, holler, scream, shout, shout out, squall, yell.

pipe up (noun)	hollo (noun)
	a very loud utterance (like the sound of an animal)

pipe up (verb)	hollo (verb)
begin to play or sing	utter a sudden loud cry
utter a shrill cry	cry hollo
	encourage somebody by crying hollo