gibber vs let loose

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

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

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

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

gibber (noun)	let loose (noun)
unintelligible talking

gibber (verb)	let loose (verb)
speak (about unimportant matters) rapidly and incessantly	express audibly; utter sounds (not necessarily words)
chatter inarticulately; of monkeys	turn loose or free from restraint