Green’s Dictionary of Slang

1. (UK und.) a bookmaker.

1895

‘G.G.’ Sporting Sketches in Sportsman (Melbourne) (18/10/1898) 5/8: ‘He laid five and six to four on the field when the square bleaters were bettin’ evens’.

2. a weakling, a whinger.

1934		Wodehouse Right Ho, Jeeves 48: A bit of a pop-eyed bleater, but on the whole clean and civil.
1978		H.C. Bosman Street-Women in Gray Theatre One 23: You seem just the same sort of bum and bleater that’s sorry for himself.

3. (US Und.) an informer.

1944		D. Runyon Runyon à la Carte 201: I figure that Schultz pegs me for a bleater.
1949		Monteleone Criminal Sl. (rev. edn).