yowl vs let loose

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

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

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

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

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

yowl (verb)	let loose (verb)
utter shrieks, as of cats	express audibly; utter sounds (not necessarily words)
cry loudly, as of animals	turn loose or free from restraint