1. A microscopic or extremely small animal, especially a protozoan or other organism visible only under a microscope.
Usage: Often used in historical or scientific contexts; somewhat archaic or formal in modern usage.

Examples

• Early naturalists used primitive microscopes to observe animalcules in pond water.
• The scientist discovered several new animalcules under the lens of her microscope.
• Animalcules were among the first living things to be studied with magnification.
• The drop of water contained countless animalcules invisible to the naked eye.
• Leeuwenhoek's observations of animalcules helped establish the field of microbiology.