Foot. A unit of length, originally the length of a man's foot. The English foot, which is in use in the United States, contains 12 inches. The feet in use in different European countries before the introduction of the metric system varied from 9 to 21 English inches. The ancient Roman foot is know to have been 11.65 English inches. Other ancient feet are of uncertain length. A foot of grindstone was formerly 8 inches. [See Metric System, Cloth Measure, Ell, Aune, Fold, Metre, Measures]