Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Micro- \Mi"cro-\, Micr- \Mi"cr-\ . [Gr. mikro`s small.] A combining form signifying:
Small, little, trivial, slight; as, microcosm, microscope.
(Metric System, Elec., Mech., etc.) A millionth part of; as, microfarad, microohm, micrometer.
Douglas Harper's Etymology Dictionary
word-forming element meaning "small, microscopic; magnifying; one millionth," from Latinized comb. form of Greek mikros "small, little, petty, trivial, slight" (see mica).
Wiktionary
pre. 1 Very small. 2 (context metric units English) One millionth.
Wikipedia
Micro- (symbol μ) is a unit prefix in the metric system denoting a factor of 10 (one millionth). Confirmed in 1960, the prefix comes from the Greek (), meaning "small".
The symbol for the prefix comes from the Greek letter μ ( mu). It is the only SI prefix which uses a character not from the Latin alphabet.
Examples:
- The size of the influenza virus is about 0.8 to 1.2 micrometres.
- Typical bacteria are 1 to 10 micrometres in diameter. Eukaryotic cells are typically 10 to 100 micrometres in diameter.