blab vs let on

blab and let on both are verbs.

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

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

blab: divulge confidential information or secrets
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

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

blab (verb)	let on (verb)
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