"would not advance a guinea"
Guinea of George III - 1795
GNU Free Documentation LicenseGuinea of George III - 1795 - Credit: Carlomorino, Wikipedia Commons

The guinea was the first machine-made gold coin, in use between 1663 and 1813. Its name came from the West African region of Guinea (not the country), from where much of the gold was sourced.

At first, one guinea was worth 1 pound, or 20 shillings. As gold prices rose, the price of the guinea fluctuated (up to 30 shillings) until in 1717 it was fixed at 21 shillings.

Long after the coin was withdrawn from circulation, prices for luxury and high class goods and services were quoted in guineas.