microorganism
Pronunciation:
/ˌmaɪ.kɹəʊˈɔː.ɡən.ɪ.zəm̩//ˌmaɪ.kɹoʊˈɔːɹ.ɡən.ɪ.zəm̩/noun
Definitions
An organism that is too small to be seen by the unaided eye, especially a single-celled organism, such as a bacterium.
Example: The cud is then reswallowed and further digested by specialized microorganisms that live in the rumen.