What is Barleycorn?

Legal Definition
A lineal measure, containing one-third of an inch. Dane's Ab. c. 211, a. 13, s. 9. The barleycorn was the first measure, with its division and multiples, of all our measures of length, superfices, and capacity. Id. c. 211, a. 1 2, s. 2.
-- Bouviers Law Dictionary
Legal Definition
In linear measure. The third of an inch.
-- Black's Law Dictionary
Legal Definition
A lineal measure, a third of an inch.
-- Ballentine's Law Dictionary