Green’s Dictionary of Slang

a gossip, an indiscreet talker.

[c.1485		‘Mary Magdalene’ Digby Mysteries II line 927: Ye brawlyng breelles, and blabyr-lyppyd bycchys] .
[c.1551		Tom Tyler and his Wife (1661) in Farmer (1908) 56: Yea, faith goodman blabberlip!].
1859		Brooklyn Eve. Star (NY) 25 Apr. 1/2: ‘Open your lips to him and I will shake your liver out of you, you young blab-mouth,’ said he, knocking me down with the poker.
1865		Newcastle Jrnl 16 May 2/5: Surprise has been expressed that Booth selected such a shallow-pated blabmouth.
1868		Burnley Advertiser 7 Sept. 3/7: Mr Blabbermouth, who is a red-hot Radical was [...] spouting at the top of his voice.
1890		Fort Worth Dly Gaz. (TX) 25 June 4/2: He would be a dandy pastor who would care to kiss that blab-mouth.
1893		Fort Worth Gaz. (TX) 28 May 6/4: You have your say, now give another fellow a chance, you blabmouther fool, you.
1910		Ottuma tri-Wkly Courier (IA) 26 May 1/4: Col. Jerome [...] criticizes James darling as a ‘blabmouth’.
1911		Big Sandy News (Louisa, KY) 14 Apr. 3/3: Mrs Essie Holbrook was calling on her sister [...] W.E. Cunningham made a business trip. [signed] Blabbermouth.
1916		Iron Co. Register (Ironton, MO) 30 Nov. 4/1: One of the gratifying results of the late campaign is the rebuke given by the [...] German-Americans to the blabber-mouths assuming to speak for them.
1936		H. Corey Farewell, Mr Gangster! 281: Kid Open Face – wonder if he is a blabbermouth or a confidence man?
1946		A. Kober That Man is Here Again 77: Blabbermouth Benny hadda go and open his big, fat puss!
1953		Kramer & Karr Teen-Age Gangs 38: I don’t want no blabbermouth letting it out.
1958		A. Fugard No-Good Friday (1993) 46: You went along to the police like any cheap blabbermouth to cause me trouble.
1968		K. Brasselle Cannibals 72: Those two blabbermouths will put it on the street real quick.
1976		J. Rosenthal Bar Mitzvah Boy Scene 18: Hey, Blabbermouth. You going to practise your speech tonight?
1986		J.B. Keane Bodhrán Makers 206: Is she a blabbermouth or is she close?
1999		Indep. Rev. 16 Oct. 9: An occupation which is, by definition, the province of any generation’s greatest accumulation of blabbermouths.
2002		A. Duff Jake’s Long Shadow 66: The taxi driver wasn’t the usual blabber mouth.
2010		D. Whish-Wilson Line of Sight [ebook] ‘[B]it of a blabbermouth when he’s stressed’.
2011		Eve. Standard 7 Apr. 22/2: She is by nature a ‘blabbermouth’.
2024		J. Meades Empty Wigs (t/s) 289: ...oh but I’m such a flighty blabbermouth my dear..