Unit Definition (centimeter)
The centimeter (or centimetre) was the basic unit of distance in the former CGS (centimeter, gram, second) version of the metric system, equal to 0.01 meter. The engineering standard uses every third power of ten, such as 10e3, 10e9, 10e12, etc., and for small numbers 10e-3, 10e-6, etc. The only exception is the centimeter. "Cent" means a hundredth, or 10e-2, but the centimeter is still commonly used because it is such a convenient unit for measuring length.

Unit Definition (inch [international, U.S.])
The inch is a traditional measurement of distance equal to 1/12 of a foot, or exactly 2.54 centimeters. The Old English word "ynce" is derived from the Latin uncia, meaning a 1/12 part. It follows that "inch" and "ounce" actually have the same origin. The inch was originally defined in England in two ways: as the length of three barleycorns laid end to end, or as the width of a man's thumb at the base of the nail. The barleycorn definition is peculiarly English, but the thumb-width definition is generic. In many european languages the word for inch actually also means thumb: examples include the Dutch duim, Swedish tum, French pouce, and Spanish pulgada. In the history of English units the inch seems to come before the foot, as after the Norman conquest of 1066, the foot was defined as 12 inches, rather than the inch being defined as 1/12 foot.