Micro- \Mi"cro-\, Micr- \Mi"cr-\ . [Gr. mikro`s small.] A combining form signifying: (a) Small, little, trivial, slight; as, microcosm, microscope. (b) (Metric System, Elec., Mech., etc.) A millionth part of; as, microfarad, microohm, micrometer. [1913 Webster]