Green’s Dictionary of Slang

indiscreet, gossiping.

1885		Sun (NY) 1 June 2/2: Shut up, you old blab-mouth fools!
1889		Sedalia Wkly Bazoo (MO) 25 June 2/1: You blab-mouthed fools, who cares what you think?
1894		Waco Eve. News (TX) 16 Jan. 3/4: A blab-mouth, curb-stone-kicker-anti-newspaper-landlord.
1895		Manchester Courier 7 Dec. 13/5: It’s the blab-mouthed sort like you as gets honest folk into mischief.
1910		Holt Co. Sentinel (Oregon, MO) 11 Mar. 1/2: A few ‘blabmouth’ partisans who belong to the past.
1922		S. Lewis Babbitt (1974) 152: These blab-mouth, fault-finding, pessimistic, cynical University teachers.
1924		Rosa Henderson ‘Don’t Advertise Your Man’ 🎵 This Tom-Swifter, / A blab-mouth sister, / Had herself a lovin’ sheik!
1928		J. Peterkin Scarlet Sister Mary 38: People would soon find out. A sin like Mary’s [...] is a blab-mouth thing.
1939		Aberdeen Jrnl 23 Oct. 1/2: Mr Churchill [...] you are the worst blabbermouthed person that ever became a Cabint Minister.
1960		W. Styron Set This House on Fire 320: Cass felt gladly shut of the blabber-mouthed bird.
1977		(con. 1949) J.G. Dunne True Confessions (1979) 107: That’s all we need [...] a blabbermouth fifteen-dollar hooker.
1999		Guardian Guide 18–24 Sept. 98: Americans fought against their natural blabbermouth tendencies.