jawbone, adj. — Green’s Dictionary of Slang

jawbone adj.

(orig. Can./US) on credit.

1918		J.E. Rendinell diary 9 July in One Man’s War (1928) 132: I won one hundred & fifty thousand jawbone franc. ‘Try & collect.’.
1930		(con. 1910s) L. Nason A Corporal Once 87: The word ‘jawbone,’ literally translated, means ‘credit’ [...] From this meaning, the word has been shaded to mean anything not complete, such as a jawbone cook, a jawbone non-com, a jawbone shavetail, etc.

In compounds

jawbone time (n.)

(US Und.) time spent in jail awaiting sentencing [i.e. ‘credit’ towards one’s jail time].

1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 28/2: JAWBONE TIME. Time spent in the guardhouse pending trial and sentence. [...] Jawbone time was not deducted from one’s sentence. [Possibly from the idea that a man is really doing time while the officers are jawing about his case.].
1949		Monteleone Criminal Sl. (rev. edn).
1956		N. Algren Walk on the Wild Side 16: They [...] boasted of their time in jail. Hard time and easy, wall time and farm time, fed time and state, city time, county time, short time and good time, soft time and jawbone time, big house, little house and middle house time, industrial time and meritorious time — ‘that’s for working your ass off’.

jawbone wedding (n.)

(US army) an informal agreement to live as man and wife.

1929

L. Thomas Woodfill of the Regulars 44: One or two fellows in the company had got married to Filipino girls in the village. There were a few others likewise who had what we called a ‘jaw-bone’ wedding — meaning just a verbal agreement without any padre to fix ’em up.