1. verb To share information that is supposed to be kept private or secret. Quit blabbermouthing everything I tell you to the whole family!
2. noun One who is prone to talking a lot and sharing such private information. I can't tell my little brother anything because he's such a blabbermouth.
blabbermouth
1. n. someone who talks too much and tells secrets. You are such a blabbermouth!
2. tv. to tell secrets in public. Don’t blabbermouth this to everybody.