Micro-

1.
a combining form with the meanings “small” (microcosm; microgamete), “very small in comparison with others of its kind” (microcassette; microlith), “too small to be seen by the unaided eye” (microfossil; microorganism), “dealing with extremely minute organisms, organic structures, or quantities of a substance” (microdissection; microscope), “localized, restricted in scope or area” (microburst; microhabitat), “(of a discipline) focusing on a restricted area” (microeconomics), “containing or dealing with texts that require enlargement to be read” (microfilm; microreader), “one millionth” (microgram).
combining form
1.
small or minute: microspore
2.
involving the use of a microscope: micrography
3.
indicating a method or instrument for dealing with small quantities: micrometer
4.
(in pathology) indicating abnormal smallness or underdevelopment: microcephaly, microcyte Compare macro- (sense 2)
5.
denoting 10–6: microsecond, μ

word-forming element meaning “small, microscopic; magnifying; one millionth,” from Latinized comb. form of Greek mikros “small, little, petty, trivial, slight” (see mica).

micro- or micr-
pref.

micro-
A prefix that means: “small” (as in microorganism) or “one millionth” (as in microsecond).

prefix