Green’s Dictionary of Slang

1. (UK Und.) one who is tricked by a confidence trickster [‘a lamb (to the slaughter)’].

1608		Dekker Lanthorne and Candle-Light Ch. 11: They that are Cheated by Jack in a Boxe, are called Bleaters.
c.1698		B.E. Dict. Canting Crew.
1719		A. Smith Lives of Most Notorious Highway-men, etc. (1926) 202: Bleaters, they that are cheated by Jack in a Box.
1725		New Canting Dict.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc.

2. a sheep or calf.

1641		R. Brome Jovial Crew II i: Here’s Grunter and Bleater, with Tib-of-the-Buttry, / And Margery Prater, all dress’d without sluttry.
a.1790		H.T. Potter New Dict. Cant (1795) n.p.: bleaters sheep.
1809		G. Andrewes Dict. Sl. and Cant n.p.: bleaters lambs, sheep.
1821		Flash Dict. [as cit. 1809].
1832		‘The Ship’s Butcher’ in Quid 203: The sheep he must attend [...] One by one the bleaters get the water.
1835		G. Kent Modern Flash Dict. 6: Bleaters – lambs, sheep.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].
1895		Penrith Obs. 23 Dec. 5/4: The shepherd [...] was minus one of his choice bleaters.

3. a sheep-stealer.

1809		G. Andrewes Dict. Sl. and Cant.
1821		Flash Dict.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].