Green’s Dictionary of Slang

1. (Aus.) working as a professional cadger.

1882		Sydney Sl. Dict. (2 edn) 6: On the Whisper - Secretly and dishonestly.
1891		Bird o’ Freedom (Sydney) 21 Mar. 5/4: Sponger was an arti't. He could get on to a man’s ear quicker’n any other cadger who lived on the ‘whisper’.

2. (UK Und.) on hire purchase.

1959

J. Gosling Ghost Squad 25: Thieves’ argot, spoken properly, is a foreign language which needs to be learned [...] ‘Get it on the whisper’ means to buy on hire purchase, (because at one time you didn’t tell the neighbours you couldn’t afford to pay cash).

1. (UK Und., also give the whisper, slip thr whisper) to ask for a loan.

1865		Leaves from Diary of Celebrated Burglar 44/1: Those among them who had been repeatedly importuned by him for the loan of a ‘tanner,’ were often obliged to ‘sling’ him the whisper for the loan of a ‘deenir.’ [Ibid.] 108/1: They [...] seldom had much ‘sugar,’ and were ever-ready to ‘sling’ the ‘whisper’ to those who were known to have ‘brought it off.’.
1905		Sporting Times 1 Apr. 3/2: What the delaval that tarantula of a landlord of mine will say when he’s given the whisper on quarter day, damfino.
1955		‘Blackie’ Audett Rap Sheet 145: A con known as Big Tiny eased up to me in the yard and slipped me the whisper.

2. (Aus./US, also chuck the whisper, whisper) to inform, to impart information.

1908		Bulletin (Sydney) 30 July 14/2: Late that night Ratto Parker chucked me th’ w’isper that th’ fancy was up at the trap-stronghold, sighin’ f’r ’er ’ero t’ bump along with a five-quid bail ’n’ freedim.
1944		C.B. Davis Rebellion of Leo McGuire (1953) 162: Even if something happened while I’m in stir so they got hep, they still wouldn’t whisper. They’s rather let the bet ride than admit they’d been boobed.
1989		J. Morton Lowspeak.