Green’s Dictionary of Slang

1. a bribe.

1592		Greene Disputation Betweene a Hee and a Shee Conny-Catcher (1923) 27: Some cowardly knaves, that for feare of the gallowes leave nipping and foysting, become crosbites; knowing there is no danger therein but a little punishment, at most the pillory, and that is saved with a little unguenteum aureum.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1801		‘Modern Dict.’ in Sporting Mag. May XVIII 102/1: The most certain cure is the unguentum aureum, not applied to the horse, but to the palm of the master of the inn, or stable.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

2. an advance payment.

1823

‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 186: Unguentum aureum — among the literati — when a bookseller advanceth money to needy authors, he is then said to apply this ‘salve for all sores’ — money.