means A precision instrument for measuring very small distances, thicknesses, or diameters, typically to thousandths of a millimeter (and a name also used for the unit of one-millionth of a meter, the micron).

from Built from the Greek 'mikros,' meaning small, and 'metron,' meaning measure — a tidy compound that does exactly what it says. The word arrived in the 17th century alongside the early scientific obsession with measuring the previously unmeasurable; the same 'mikros' lurks in microscope, microbe, and microphone, all members of a family devoted to the very tiny.