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

Healthy soil relies on these microorganisms to break down nutrients and support plant roots. —Sj McShane, Martha Stewart, 31 May 2026

Pasteurization kills all microorganisms, including probiotics. —Merve Ceylan, Health, 29 May 2026

The setup allowed continuous hydrogen production while the microorganisms still carried out photosynthesis under light exposure. —Aamir Khollam, Interesting Engineering, 27 May 2026

Depending on soil temperature and moisture, the number of microorganisms in the soil, and the carbon content of the wastes, decomposition will occur in one month to one year to feed plant root systems. —Mary Marlowe Leverette, Southern Living, 24 May 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