Definition of microorganism
: an organism (such as a bacterium or protozoan) of microscopic or ultramicroscopic size
Recent Examples of microorganism from the Web
The composting process employs billions of microorganisms to break down organics into the essential component of soil called humus.
Known to have a low concentration of nutrients, the Sargasso was also assumed to harbor relatively few microorganisms.
These example sentences are selected automatically from various online news sources to reflect current usage of the word 'microorganism'. Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
Origin and Etymology of microorganism
International Scientific Vocabulary
First Known Use: 1880See Words from the same year
MICROORGANISM Defined for English Language Learners
Definition of microorganism for English Language Learners
biology : an extremely small living thing that can only be seen with a microscope
MICROORGANISM Defined for Kids
Definition of microorganism for Students
: a living thing (as a bacterium) that can only be seen with a microscope
Medical Definition of microorganism
: an organism of microscopic or ultramicroscopic size
Seen and Heard
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