let on vs blab

let on and blab both are verbs.

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

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

let on: 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 on (verb)	blab (verb)
make known to the public information that was previously known only to a few people or that was meant to be kept a secret	divulge confidential information or secrets
	speak (about unimportant matters) rapidly and incessantly