yowl vs let out

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

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

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

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

yowl (noun)	let out (noun)
a very loud utterance (like the sound of an animal)

yowl (verb)	let out (verb)
utter shrieks, as of cats	make (clothes) larger
cry loudly, as of animals	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