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

Chlorine is added to disinfect and UV radiation helps kill off additional microorganisms. —Sophie Hartley, IndyStar, 26 Jan. 2026

Showing that animal behavior can selectively shape what types of microorganisms are living on their fur or inside their guts can help researchers understand how actions that influence animal health evolved. —Laura Baisas, Popular Science, 21 Jan. 2026

This, in turn, causes inadequate air supply to root systems and loss of beneficial microorganisms. —Barbara Gillette, The Spruce, 15 Jan. 2026

Pasteurization kills all microorganisms, including probiotics. —Merve Ceylan, Health, 15 Jan. 2026

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Rhymes for microorganism

• absolutism
• adventurism
• aestheticism
• africanism
• agnosticism
• alcoholism
• anabolism
• anachronism
• anglicanism
• antagonism
• arianism
• asceticism

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