Green’s Dictionary of Slang

blabber n.

[blab n.]

1. [1920s] a newspaper.

2. [1940s–70s] the mouth.

SE in slang uses

In compounds

blabberguts (n.) [-guts sfx]

[1910s] (US) a gossip.

blabberskite (n.) [var. on SE blatherskite]

[2000s] a voluble, boastful speaker.