Added 9 October 2026 microorganism /ˌmaɪ.kɹəʊˈɔː.ɡəˌnɪz.m̩/ noun Categories: AnimalsRare Words noun ! Definition from Wiktionary (CC BY-SA). Pronunciation from Wiktionary, via Kaikki.org. More about microorganism at Wordnik → Where our words come from → An organism that is too small to be seen by the unaided eye; especially, a single-celled organism, such as a bacterium. The cud is then reswallowed by the ruminant and further digested by specialized microorganisms that live in the rumen. Related Words: microbialmicro-organismmicrobeorganismmicrobiologyaerobegermbugdepositresistancecandidatepatent Back to today's word