The Collaborative International Dictionary
Micr-
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.
Wiktionary
micr-
pre. (alternative form of micro- English) (qualifier: before a vowel)