Green’s Dictionary of Slang

1. to betray.

1862		in Southern Historical Society P. (1884) XII 272: Boys, your game is up — Busy Bill gave it away [DA].
1872		E. Crapsey Nether Side of N.Y. 55: Two men from the same [private detective’s] office are often detailed to ‘shadow’, one the husband and the other the wife, and it occasionally happens that they do a little business on private account by ‘giving away’ each other. That is to say, the husband’s man informs the wife she is watched, and gives her a minute description of her ‘shadow’ for which information he of course gets an adequate reward, which the wife’s man likewise earns and receives by doing the same kindly office for the husband.
1882		Dly Dispatch (Richmond, VA) 1 Nov. 3/3: Thieves [...] have no use for a ‘croaker’, or a newspaper that ‘gives them away’.
1885		Bulletin (Sydney) 15 Aug. 18/1: Being pressed by the Court she whispered the reason in the judge’s ear, and he ungallantly ‘gave it away.’ The lady had false teeth and she was afraid if she allowed her husband to press her lips he would discover her secret.
1890		Boston Journal 21 Nov. 2/3: A Cincinnati teamster [...] gave away his brother-in-law, who was a deserter from the regular army, and thereby scooped in $30 in cash [DA].
1890		Sporting Times 12 Apr. 1/4: [He] finds that some good-natured friend has ‘given him away’ to the wife of his bosom, and sent her the address of the dear girl he came across at Christmas.
1895		Herald (Melbourne) 27 Aug. 2/7: He was still cautious, and thought I might ‘give him away.’ I assured him that I would not, and he accepted the assurance.
1900		Sporting Times 21 Apr. 1/3: [He had] been given away by some anonymous skunk to the wife of his bosom, who now has the name and address of the sweet little thing he took to the Boat Race.
1908		‘Doss Chiderdoss’ ‘Significant Strains’ Sporting Times 9 May 1/3: The presence close at hand / Of two feminines, the housemaid and the cook / Gave the game away sufficiently to make us understand / Why they chanced to be so handy on the ‘hook’.
1925		Wodehouse Carry on, Jeeves 170: Even at the expense of giving old Sippy away, I must be cleared of this frightful charge. After all, Sippy’s number was up anyway.

2. (Aus.) to give up, to abandon, to forsake.

1885		Bulletin (Sydney) 6 June 17/2: But the wonder to me is why these dentists, with all their talent, continue to ‘give their patients away’ – Charlie’s slang phrase – in such a stupid wholesale manner as they do.
1972		G.W. Turner Eng. Lang. in Aus. and N.Z. 107: Some very common Australianisms [...] to give something away, ‘to give up or abandon an activity’.