Blab and Let out

Blab verb - Divulge confidential information or secrets.

Let out is a synonym for blab in show topic. In some cases you can use "Let out" instead a verb "Blab", when it comes to topics like gossip, blurt out.

Let out verb - Express audibly; utter sounds (not necessarily words).

Blab is a synonym for let out in reveal topic. You can use "Blab" instead a verb "Let out", if it concerns topics such as utter suddenly.