Green’s Dictionary of Slang

blab n.

[blab and its v. forms blab and, apparently, blabber are the first sl. terms relating to speech and can be found as such in the 16C. Their history, however, is somewhat older. There is even, according to the OED, a question whether what appears to be an obvious link actually exists. Blab, then spelt blabbe and meaning a ‘chatterer’, occurs in Chaucer c.1374; blab, meaning simply ‘chatter’ or ‘loose talk’, can be found in The Tale of Beryn (c.1400), but then promptly vanishes until the 16C, when it is augmented by a v. form, blab, to chatter (1535). This, in turn, creates a n., blabber, a chatterer. However, the v. blabber predates all these; it occurs in Piers Ploughman (1362) and, with its n. blabberer, is common in the works of John Wyclif (1330–84). Thus, however tempting it may seem, one cannot simply assume that blab is a 14C abbr. of blabber. Instead, the OED suggests, it is related to the noun labbe, a revealer of secrets, in Chaucer, and the verb labbe in Piers Ploughman and to labbyng, open-mouthed. It can also be linked to the Old Dutch labben, to chatter. Thus blab/blabbe might be a mixture of labbe and blabber; but might also be simply onomat.]

1. a tell-tale.

[UK]Nice Wanton Aiiii: That knauve your brother wyl be a blabbe styll.
[UK]T. Tusser Five Hundred Pointes of Good Husbandrie (1878) 190: Backbiting talk that flattering blabs know wily how to blenge.
[UK]S. Gosson School of Abuse (1868) 24: I shoulde tel tales out of the Schoole, and bee [...] hyssed at for a blab.
[UK]Florio Worlde of Wordes n.p.: Gracchia, [...] Also a blab, a prater, a tatler.
[UK]W. Haughton English-Men For My Money III ii: And, sirrah Frisco, see you prove no blab.
[US]N. Whiting Albino and Bellama 138: Peace huswife, sayes mine host, you tatling blab.
[UK]Horn & Robotham (trans.) Gate of Languages Unlocked Ch. 86 838: A blab (a long-tongue) bewrayeth (discloseth) and blabbeth out secrets.
[UK]W. Davenant Man’s the Master III i: I can keep secrets [...] I never tell for fear men should take me for a blab.
[UK]J. Ray Proverbs 63: He that is a blab, is a scab.
[UK]Congreve Love for Love IV i: I am no blab, sir.
[UK]M. Pix Adventures in Madrid I i: She cries Men of your Country are such Blabs, and one step towards Discovery for ever loses her.
[UK]J. Addison Drummer V i: You need not be a blab.
[UK]Bailey (trans.) Erasmus’ Colloquies 479: Have you got a Blab of a Servant then?
[UK]Bailey Universal Etym. Eng. Dict.
[UK]Spy on Mother Midnight 13: They begin not to be sham’d of an Intrigue, and to be as great Blabs as any Lay-Rake of them all.
W. O’Brien Cross Purposes in Coll. Farces & Entertainment VI (1788) 58: Hush, you confounded blab.
[UK]Grose Classical Dict. of the Vulgar Tongue.
[UK]R. Porson ‘Imitation of Horace’ in Whibley In Cap and Gown (1889) 67: You know I never was a blab.
[UK]B.H. Malkin (trans.) Adventures of Gil Blas (1822) I 133: I should never had known, but for that blab Inésilla.
[UK]Lex. Balatronicum.
Vidocq Memoirs (trans. McGinn) III 110: Why should I tell you? you women are all blabs.
[UK] ‘A Merry Christmas’ Bentley’s Misc. Mar. 266: I see you have got hold of some of our family secrets; but Seaforth was always a blab.
[UK]Sam Sly 20 Jan. 3/2: He advises Mr. T—s W—g [...] to be very cautious in the selection of his bosom friends, for the one he has chosen is a blab.

2. talk.

[[UK]G. Harvey Pierce’s Supererogation 145: It is a blabb: but not euery mans blabb, that casteth a sheepes-eye out of a Calues-head; but a blabb with iudgement; but a blabb, that can make excrements blush.].
[US]W.H. Thomes Bushrangers 298: Men of the bush had but little respect for each other, and were not fond of what they called ‘blab’.
[UK]W. Eyster Far from the Customary Skies 32: Shut the blab.
[US](con. 1940s–60s) Décharné Straight from the Fridge Dad.

In derivatives

blabfest (n.) [-fest sfx]

(US) a gathering where those involved devote themselves to talking, esp. unashamed gossip.

[US]D.A. Kinsley Death Rides a Camel 363: The Prime Minister, as usual, was a one-man blabfest all during dinner.
[US]R. Girardi Madeleine’s Ghost 235: I go for ten years without a word and you show up and it’s one long blabfest.
[US]J.A. Klein Global Deception 68: It’s far more fun to hang out with Mick and Bill and Hill [...] at some UN-sponsored blabfest.

In compounds

In phrases

blabs in labs (n.)

(US campus) a course in linguistics, the ‘labs’ are language laboratories.

[US]L. Birnbach Official Preppie Hbk.
[US]W. Safire What’s The Good Word? 300: Students of linguistics engage in ‘Blabs in Labs’.
[US]John Burkardt ‘Lucky Duck’ Wordplay [Internet] blabs in labs (a college linguistics course).