1. microscopic single-celled organisms, especially ciliated protozoans, that are commonly found in infusions of organic matter
Usage: biology; archaic

Examples

• The scientist observed infusorians swimming in the pond water sample.
• Infusorians were among the first microorganisms studied under early microscopes.
• The hay infusion contained numerous infusorians after several days.
• Paramecia are common examples of infusorians found in stagnant water.
• The biology textbook described infusorians as primitive single-celled animals.