microorganism

noun

mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌni-zəm 

: an organism (such as a bacterium or protozoan) of microscopic or ultramicroscopic size

Examples of microorganism in a Sentence

Recent Examples on the Web

Because microorganisms in water turn regular mercury into methylmercury, a toxic chemical form that binds tightly to fish tissue, the heavy metal accumulates to higher levels in aquatic animals. — Sandee Lamotte, CNN Money, 2 Oct. 2026

According to the company, the ingredient creates pathways that allow naturally occurring microorganisms to break down the polymer in environments with the conditions needed for biodegradation. — Alexandra Harrell, Footwear News, 2 Oct. 2026

The hot water gushing into an isolated region of the freezing depths could have attracted microorganisms and possibly other life forms that were otherwise struggling to survive. — Elizabeth Rayne, ArsTechnica, 30 Sep. 2026

The microorganisms grow best in low-oxygen conditions and require specific pH conditions. — Adam Kovac, Scientific American, 28 Sep. 2026

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Rhymes for microorganism

• activism
• albinism
• altruism
• aneurism
• animism
• aphorism
• atomism
• barbarism
• bolshevism
• botulism
• brahmanism
• calvinism

Kids Definition

microorganism

noun

mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌniz-əm 

: an organism (as a bacterium) of microscopic or less than microscopic size

Medical Definition

microorganism

noun

mi·​cro·​or·​gan·​ism -ˈȯr-gə-ˌniz-əm 

: an organism of microscopic or ultramicroscopic size