mil

   1. a unit of distance equal to 0.001 inch: a "milli-inch," in other words.

   Mils are used, primarily in the U.S., to express small distances and tolerances in engineering work. One mil is exactly 25.4 microns, just as one inch is exactly 25.4 millimeters. This unit is also called the thou. With the increasing use of metric units in the U.S., many machinists now avoid the use of "mil" because that term is also a handy slang for the millimeter.

   2. a unit of angle measure, used in the military for artillery settings. At one time the U. S. Army used a mil equal to 1/1000 of a right angle, 0.1 grad, 0.09°, or 5.4 arcminutes (often written 5.4 moa; see "moa" below). Later this was changed to 1/1600 right angle, or 0.05625° (3.375 moa). In target shooting, the mil is often understood to mean 0.001 radian or 1 milliradian, which is about 0.0573° or 3.43775 moa. In Britain, the term angular mil generally refers to the milliradian. 1 milliradian corresponds to a target size of 10 millimeters at a range of 10 meters, or 3.6 inches at 100 yards.

   3. a common slang name for the milliliter (mL) or the millimeter (mm).

   4. in Scandinavia, the mil, pronounced like "meal" in English, is a traditional distance unit considerably longer than Roman or English miles. In Denmark, the traditional mil was 24 000 Danish feet, which is 4.6805 miles or 7.5325 kilometers (this is the same as the north German meile; see above). The Danish mil has sometimes been interpreted as exactly 7.5 kilometers (4.6603 miles). In Sweden, the traditional mil was 36 000 Swedish feet, which is 6.641 miles or 10.687 kilometers. In Sweden and Norway the mil is now interpreted as a metric unit equal to exactly 10 kilometers (6.2137 miles).

   5. an alternate spelling of the mill¹.