let out vs blab

let out and blab both are verbs.

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

As verbs, blab is a hyponym of let out; that is, blab is a word with a more specific, narrower meaning than let out:

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
blab: divulge confidential information or secrets

let out (verb)	blab (verb)
make (clothes) larger	divulge confidential information or secrets
make known to the public information that was previously known only to a few people or that was meant to be kept a secret	speak (about unimportant matters) rapidly and incessantly
express audibly; utter sounds (not necessarily words)
bring out of a specific state