gibber vs let out

gibber is a noun but let out is not a noun.

Word	Noun	Adjective	Verb	Adverb
gibber	Yes	No	Yes	No
let out	No	No	Yes	No

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

Other hypernyms of gibber include emit, let loose, utter.

gibber (noun)	let out (noun)
unintelligible talking

gibber (verb)	let out (verb)
speak (about unimportant matters) rapidly and incessantly	make (clothes) larger
chatter inarticulately; of monkeys	make known to the public information that was previously known only to a few people or that was meant to be kept a secret
	express audibly; utter sounds (not necessarily words)
	bring out of a specific state