A coin of account is a unit of money that does not exist as an actual coin (that is, a metal disk) but is used in figuring prices or other amounts of money.
The mill (or sometimes, mil) is a coin of account in the United States.
It is equal to one-tenth of a penny, and so to one-thousandth of a dollar (= $0.001), whence the name, which means "thousandth."
From 1816 to the 1980s the British Guinea was no longer used a coin but prices for luxury items and professional services were often quoted in guineas, on the understanding that a guinea was equal to 21 shillings.
This money or currency-related article is a stub.