baa vs let out

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

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

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

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

baa (noun)	let out (noun)
the cry made by sheep

baa (verb)	let out (verb)
cry plaintively	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