What does microorganism mean?
A microorganism is an organism too small to be seen clearly with the unaided eye. The category includes bacteria, archaea, microscopic fungi, and protozoans, and medical usage may also treat viruses as microorganisms, although viruses are not generally classified as living organisms. Microorganisms occur almost everywhere, from soil, water, and air to the human body, and they play both beneficial and harmful roles. Some decompose organic matter, help produce food, or support the health of larger organisms, while others cause infections and disease. Scientists study microorganisms with tools such as microscopes and cultures, using laboratory techniques to identify them and determine their effects. The word is especially common in biology, medicine, food science, and environmental studies, where it provides a more formal alternative to the everyday term microbe.
nounA living organism of microscopic size, especially one such as a bacterium, archaeon, fungus, or protozoan. The term is also used more broadly for microscopic infectious agents, including viruses.
- A microscopic living organism, especially a bacterium, archaeon, fungus, or protozoan.
- A microscopic infectious agent, including a virus, considered in a medical or biological context.
"The laboratory tested the sample for harmful microorganisms before using it to culture the cells."
"The researcher identified several microorganisms in the soil samples collected near the river."
"Careful food preparation helps prevent microorganisms from causing spoilage or illness."
The standard plural is “microorganisms.” The singular form is commonly used collectively to refer to microscopic life in general.
"The cleaning product kills microorganisms commonly found on kitchen surfaces."
The smallest living things on Earth are microorganisms, and a single drop of water can contain more of them than there are people on the planet.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of microorganism
The word was formed in the 19th century by combining the combining form micro-, derived from Greek mikros, meaning “small,” with organism, from Greek organos, meaning “instrument” or “organism.” Its development reflects the period's growing ability to observe and study microscopic life through improved microscopes. The element also connects it with terms such as microscope, microbe, and microbiology.
Related word forms
How microorganism is actually used
In scientific and medical contexts, microorganism is a neutral technical term. In everyday use, it often emphasizes disease-causing agents, although it can refer equally to beneficial organisms.
Easily confused with microorganism
A microbe is a familiar, often broad term for a microorganism, while microorganism is more technical and is especially common in biology, medicine, and environmental science.