Green’s Dictionary of Slang

1. a certainty.

1882		Maryborough Chron. (Qld) 8 July 5/4: The Maoris have too often come down like wolves upon the Australian fold, to expect anything like a chuck in; but there is some doubt of the excellence of the New Zealand form.
1890		Bulletin (Sydney) 12 July 15/1: Some of the reputed goers have gone already. St Louis, for whom the Grand National Hurdle was a ‘chuck in,’ has been chucked out.
1903		Bulletin (Sydney) 10 Dec. 18/3: I seed a quart standin’ alongsider Fred, an’ what wuz more it wuz full o’ water. I thinks to myself, ’ere’s a chuck-in, an’ put it to my lips [...].
1912		Bulletin (Sydney) 5 Sept. 9/1: Well, per’aps that’s all true, an’ they ses that I knoo / They wus pinched when I made ’im the bid. / It ’ud be a fair sin fer to miss that chuck in; / So I arsts: Wot’s the odds if I did?

2. a piece of good fortune; a bargain; an advantage.

1887		Queenslander (Brisbane) 14 May 767/3: The fact is the local horses have not had the ‘chuck in’ they formerly enjoyed, and outsiders now have a show for some of the chief prizes.
1902		North Queensland Register (Townsville, Qld) 18 Aug. 6/1: Maxwelton will have cut out by that time, and this will be a chuck in for the shearers and rouseabouts.
1904		Sun. Times (Perth) 31 Jan. 1/1: Pinjarra property-owners have a chuck-in in living near Roads Board M’Larty. While the mileage to Mandurah resembles a mulga track, carriage drives occur round Mac’s mansion.
1910		Northam Advertiser (WA) 8 June 2/1: CUNDERDIN— 850 acres, fenced six wires, lot cleared, best land. A ‘chuck in’ at £2/5/- per acre.
1914		Moora Herald (WA) 28 Apr. 2/6: As is usually the case each player thinks some of the others have a ‘chuck in,’ to use a billiard-room classic, but everybody enters just the same, and in his mind each thinks be has a bare fighting chance.
1932		Telegraph (Brisbane) 21 Sept. 14/6: [advert] A HOME within five minutes of Queen Street, close Lelchhardt Street school. 6 rooms, sewerage. 50 ft. frontage, accept £350 cash, a chuck In for someone.

3. a bonus.

1901

Leader (Melbourne) 12 Oct. 19/3: The big lode in the North Woah Hawp mine, Ballarat East, is showing signs of further improvement, and the ‘chucks in’ which the company frequently obtains from the indicator in the shape of nuggets, add in no small measure to the golden outputs.

4. a voluntary subscription.

1945		Baker Aus. Lang.
1959		D. Stuart Yandy 58: Mitchell counted the chuck-in of money, and said ‘Fifty-seven shillings.’.