/ Dictionary / Index M microorganism: Meaning and Definition of Find definitions for: mi•cro•or•gan•ism Pronunciation: (mī"krō-ôr'gu-niz"um), [key] — n. any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: microorganism (Thesaurus) micronutrient micropaleontology Related Content Daily Word Quiz: censure Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language