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

Most of the food comes ready to eat, having been rehydrated, thermostabilized using heat to destroy harmful microorganisms and enzymes, or irradiated to kill bacteria. —Eric Lagatta, USA Today, 26 Mar. 2026

Bare soil leads to erosion, nutrient deficiencies, moisture loss and the death of microorganisms. —ABC News, 23 Mar. 2026

Some of that carbon ends up in leaves, stems, and flowers, and some is sent belowground to build roots and feed soil microorganisms. —Dr. Avishesh Neupane, Hartford Courant, 21 Mar. 2026

The movie explores a few unique forms that extraterrestrial life could take, from space microorganisms that produce both infrared light and an unfathomable amount of energy, to rocklike aliens that live under crushing pressure and breathe ammonia. —Mary Magnuson, The Conversation, 20 Mar. 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