Webster's Revised Unabridged Dictionary · 1913

Micro-

Micro-

[Greek mikro`s small.]

(Metric System, Electricity, Mechanics, etc.) A combining form
(a)
(Metric System, Electricity, Mechanics, etc.) Small, little, trivial, slight; as, microcosm, microscope.
(b)
(Metric System, Electricity, Mechanics, etc.) A millionth part of; as, microfarad, microohm, micrometer.

Also: Micr-