quack vs let loose

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

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

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

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

quack (noun)	let loose (noun)
the harsh sound of a duck
an untrained person who pretends to be a physician and who dispenses medical advice

quack (adjective)	let loose (adjective)
medically unqualified

quack (verb)	let loose (verb)
act as a medical quack or a charlatan	express audibly; utter sounds (not necessarily words)
utter quacking noises	turn loose or free from restraint