blab vs let out

blab and let out both are verbs.

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

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

blab: divulge confidential information or secrets
let out: make known to the public information that was previously known only to a few people or that was meant to be kept a secret

Other hypernyms of blab include break, bring out, disclose, discover, divulge, expose, give away, let on, reveal, uncover, unwrap.

blab (verb)	let out (verb)
divulge confidential information or secrets	make (clothes) larger
speak (about unimportant matters) rapidly and incessantly	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