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decad

A unit of length proposed by Thomas Jefferson in 1790¹, for use if the new United States decided to adopt a decimal system of lengths. After defining a rod such that one-fifth of it was a foot (“about one quarter of an inch shorter than the present foot”), Jefferson suggested:

Let the foot be divided into 10 inches;

The inch into 10 lines;

The line into 10 points;

Let 10 feet make a decad;

10 decads one rood;

10 roods a furlong;

10 furlongs a mile.

1. Thomas Jefferson, Secretary of State.
Plan for establishing uniformity in the Coinage, Weights, and Measures of the United States.
Communicated to the House of Representatives, July 13, 1790.