Green’s Dictionary of Slang

of a chatterer, a gossip, one who is unable to keep a secret; thus as long-tongued as Granny [‘Granny was an (actual) ideot (sic) who could lick her own eye’ (Grose)]; have a long tongue, to be a chatterer or gossip.

1592		Shakespeare Titus Andronicus IV ii: ’Tis a deed of policy: Shall she live to betray this guilt of ours, A long-tongu’d babbling gossip?
1602		J. Cooke How A Man May Choose A Good Wife From A Bad Act III: She blusht & said that long tong’d men would tell.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Long Tongued. Loquacious, not able to keep a secret. He is as long-tongued as Granny: Granny was an idiot who could lick her own eye.
1811		Lex. Balatronicum [as cit. 1788].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1788].
1837		R. Barham ‘Look at the Clock’ Ingoldsby Legends I (1866) 31: Mrs. Pryce was not over young, Had very short legs and a very long tongue.
1867		J. Poole Ye Comedie of Errors I i: She’s got a long tongue, as you’ll find out when she’ll scold.
1873		Royal Cornwall Gaz. 20 Sept. 6/4: The regulations are intended to prevent [...] the betrayal of trust, if [...] a longue-tongued clerk tittle-tattles.
1881		Dundee Courier 27 Jan. 2/3: Long-tonuged orators who are bent on getting Home Rule by obstructing ordinary business.
1888		Shields Dly Gaz. 6 Aug. 3/2: This, however, will be disputed by men who have long-tongued wives.
1900		Bulletin (Sydney) 2 Jun. 31/2: ‘You never told him, I’ll go bail. But it would hardly do.’ / She winced. The door was open, and Smith had such a long tongue.
1902		Rice Belt Jrnl (Calcasieu Parish, LA) 4 July 1/4: These [...] long-tongued, back-biting Christians.
1916		Day Book (Chicago) 20 Mar. 9/2: There are a few old long-tongued tattling women.
1920		Hayti Herald (MO) 30 Dec. 2/1: These derogatory statements are originated by the malicious, who intend that they shall be circulated by [...] the common long-tongued variety of gossips.
1946		Cornishmen 23 May n.p.: Mrs Longuetongue, whose business is everybody’s business [and] the gossip’s male counterpart, Mr Gasbag.
1947		W.D. Overholser Buckaroo’s Code (1948) 52: A smart alec, long-tongued, sashay-dude like you.
1959		D. Niland Gold in the Streets (1966) 121: There’s another dame I could murder: long-tongued lizard.