Middle English (Scots), from Scottish Gaelic innis
First Known Use: 15th century
Medical Definition of INCH
: a unit of length equal to 1⁄36 yard or 2.54 centimeters
Unit of measure equal to 1/36 yard and since 1959 defined officially as 2.54 cm (seemetre). David I of Scotland (c. 1150) defined the inch as the breadth of a man's thumb at the base of the nail; usually the thumb breadths of three menone small, one medium, and one largewere added and then divided by three. During the reign of England's Edward II, the inch was defined as three grains of barley, dry and round, placed end to end lengthwise. At various times it has also been defined as the combined lengths of 12 poppy seeds. See alsofoot; International System of Units; measurement; metric system.