miaou vs let out

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

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

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

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

miaou (noun)	let out (noun)
the sound made by a cat (or any sound resembling this)

miaou (verb)	let out (verb)
make a cat-like sound	make (clothes) larger
	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