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

Yogurt Many types of yogurt contain probiotics, which are live microorganisms that may provide health benefits (when consumed in adequate amounts). —Trista Chan, Health, 12 June 2026

Fatigue The bacteria and other live microorganisms in your gut, known as the gut microbiome, can affect your energy levels. —Carrie Madormo, Verywell Health, 11 June 2026

Woody mulch moderates soil temperature and encourages healthy soil microorganisms. —Andy Wilcox, Better Homes & Gardens, 9 June 2026

This includes decaying plant and animal residues, humus, and living microorganisms. —Rae Ford, Martha Stewart, 8 June 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