Microorganism
/mˌaɪkroʊˈɔrɡəˌnɪzəm/
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Definition
(noun) An organism that is too small to be seen by the unaided eye; especially, a single-celled organism, such as a bacterium.
Sentence Examples
Tom succeeded in culturing the new microorganism.
The alien microorganism grew faster.
CEFR Practice Quiz
A single ____ can be seen under a strong microscope, revealing a complex world of biological activity invisible to the naked eye.