blab 
(blăb)
(blăb)v. blabbed, blab·bing, blabs
v.tr.
To reveal (secret matters), especially through indiscreet or unreserved talk.
v.intr.
1. To reveal secret matters indiscreetly.
2. To chatter thoughtlessly or indiscreetly.
n.
1. An incessant or indiscreet talker.
2. Lengthy chatter.
[Middle English blabben, to talk foolishly, back-formation from blaberen.]
blabby adj.