A tiny or microscopic animal, especially one too small to see without a microscope; a very small living creature.
From Latin 'animalculus,' a diminutive of 'animal,' meaning 'little animal.' Diminutives were common in Latin to express small size, and English borrowed this during the Scientific Revolution.
When microscopes were invented in the 1600s, scientists called what they saw 'animacules'—including sperm, bacteria, and protozoans—because they thought everything tiny was an animal.
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