• prefix
    (written as micro-)
    one millionth of a unit


  • (written as micro-)
    A metric prefix representing 10-6, or one millionth. For instance, 1 microampere is equal to 10-6, or one millionth of an ampere. Its abbreviation is μ, or less commonly, mc.


  • prefix
    (written as micro-)
    small or minute, or using a microscope or requiring magnification

Information & Library Science

  • prefix
    (written as micro-)
    used to indicate a very small version of anything

Origin & History of “micro”

The conversion of the prefix micro- into a noun (standing, for instance, for a microskirt or microcomputer) is not as recent as one might have supposed: as long ago as the 1860s it was being used for a sort of tiny moth (short for microlepidoptera). The prefix itself comes from Greek mīkrós ‘small’, a variant of smīkrós, which may be distantly related to English small. The earliest English word containing it appears to have been microcosm (15th c.), etymologically ‘little world’. From the 17th century come micrometer, microphone, and microscope. Microbe (19th c.) means etymologically ‘little life’ (from Greek bíos ‘life’), hence ‘little creature’.