Green’s Dictionary of Slang

1. (orig. Can./US) credit.

1862		Times 21 Oct. (San Francisco Correspondent) n.p.: Individuals, who, in digger’s parlance, live on jawbone.
1865		M. MacFie Vancouver Island and British Columbia 416: Credit is ‘jaw-bone,’ and in one store on the road to Cariboo, the fullsize jaw-bone of a horse is polished, and suspended on the wall, with the words written under: ‘None of that allowed here.’.
1900		Nation 4 Oct. LXXI 270/1: A common slang among American soldiers for the word ‘credit’ is ‘jawbone’ [DA].
1918		L.E. Ruggles Navy Explained 83: To get credit was to get jawbone.
1926		Maines & Grant Wise-crack Dict.
1930		‘Dean Stiff’ Milk and Honey Route 24: They got their tobacco and chuck, and credit in the company store, but nothing more. Credit like that was known as ‘Jawbone’.
1940		Phila. Eve. Ledger 20 July n.p.: ‘Jaw bone’ – credit. It’s one of the most well-used terms in the army and means doing a lot of talking to borrow anything from a cigarette to a dollar.
1947		D.W. Hamilton ‘Pacific War Lang.’ in AS XXII:1 Feb. 55: jawbone. Credit.
1952		J. Jones From Here to Eternity (1998) 222: ‘We could play for jawbone,’ Prew grinned. ‘I cant. I owe my payday out already.’.

2. (US) empty talk, exaggerated promises that are not kept.

1873		Overland Monthly (CA) Feb. 108: The interlopers [...] signified their intention of ‘camping right there until the Doctor was prepared to come down with a little jaw-bone.’.
1894		Truth (Sydney) Feb. 1/1: ‘Truth’ Thinks [...] That the House should be careful about again following the lead of Jawbone Neild.
1898		Voice (N.Y.) 24 Mar. 4/1: Jawbone is cheap, and there is plenty of it; backbone is something rare [DA].
1901		Sydney Sportsman (Surry Hills, NSW) 5 June 1/8: Holy Joe Cook in the House of Reps and Jawbone Nield in the senate.
c.1943		‘Bill O. Lading’ You Chirped a Chinful!! n.p.: Jawbone: A soldier great on theory but poor on practice.
1953		Chronicle-Telegram (Elyria, OH) 29 Sept. 5/5: ‘Livin’ on his jawbone’ is an expressive way of describing a blow-off.
1967		M. Braly On the Yard (2002) 207: When Stoneface had you he didn’t waste time on jawbone.