protozoan

American  

[proh-tuh-zoh-uhn] / ˌproʊ təˈzoʊ ən /

noun

protozoans, plural protozoa plural

1. any of a diverse group of eukaryotes, of the kingdom Protista, that are primarily unicellular, existing singly or aggregating into colonies, are usually nonphotosynthetic, and are often classified further into phyla according to their capacity for and means of motility, as by pseudopods, flagella, or cilia.

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adjective

1. of, relating to, or characteristic of a protozoan.

protozoan British  

/ ˌprəʊtəˈzəʊən /

noun

1. Also called: protozoon.  any of various minute unicellular organisms formerly regarded as invertebrates of the phylum Protozoa but now usually classified in certain phyla of protoctists. Protozoans include flagellates, ciliates, sporozoans, amoebas, and foraminifers

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adjective

1. of or relating to protozoans

protozoan Scientific  

/ prō′tə-zō′ən /

protozoans plural

1. Any of a large group of one-celled organisms (called protists) that live in water or as parasites. Many protozoans move about by means of appendages known as cilia or flagella. Protozoans include the amoebas, flagellates, foraminiferans, and ciliates. Their traditional classification as the subkingdom Protozoa is still used for convenience, but it is now known that protozoans represent several evolutionarily distinct groups.

2. See more at protist

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Other Word Forms

Noun Inflected Forms

• protozoa
  plural
• protozoans
  plural

Etymology

Origin of protozoan

First recorded in 1860–65; Protozo(a) + -an

Example Sentences

See Examples For:

protozoan protozoa protozoans

Giardia duodenalis is a microscopic protozoan parasite known for causing outbreaks of severe diarrhea.

From Science Daily ● Dec. 21, 2025

A research team placed Halteria ciliates—a type of protozoan with hairlike organelles found in freshwater worldwide—in a petri dish with only chloroviruses, which infect green algae.

From Science Magazine ● Jan. 11, 2023

By taking a deeper look at how this stealthy protozoan travels through our anatomy, we can develop better tools at disrupting its devastating pathways.

From Salon ● Nov. 1, 2022

One common protozoan disease known to occur in birds, which evolved from feathered dinosaurs, as well as in people is called trichomoniasis, caused by a parasitic protozoan.

From Reuters ● Oct. 1, 2022

There is another protozoan, called blepharisma, telling a long story about the chanciness and fallibility of complex life.

From "The Lives of a Cell" by Lewis Thomas

The host of life on ice includes bacteria, viruses, fungi, protozoa, even microscopic animals like nematodes, some dead and some alive in suspended animation.

From Salon ● Apr. 24, 2025

Bottom line: If you must have tropical milkweed, cut it down to the ground each fall before it goes to seed, to kill any overwintering protozoa and reduce its potential to spread to neighboring areas.

From Los Angeles Times ● Oct. 30, 2023

Food turns into compost through the hard work of small microorganisms like bacteria, fungi, and protozoa.

From National Geographic ● Sep. 26, 2023

You should make sure that you use only distilled, sterile or boiled water for your rinses, as tap water can contain small amounts of bacteria and protozoa that carry the risk of other infections.

From Seattle Times ● Oct. 31, 2022

Insects are beset not only by viruses and bacteria but also by fungi, protozoa, microscopic worms, and other beings from all that unseen world of minute life that, by and large, befriends mankind.

From "Silent Spring" by Rachel Carson

The researchers explored whether the holes had been caused by an infection involving microbes called protozoans.

From Reuters ● Oct. 1, 2022

The broadest definition of “parasite” includes pathogens such as bacteria, viruses, fungi and protozoans.

From Scientific American ● May 18, 2022

Researchers also have identified the single-celled species that are the closest relatives to the animal kingdom — tiny aquatic protozoans that prey on bacteria.

From New York Times ● May 4, 2018

And just like a tapeworm or malaria protozoans, it doesn’t care if it disables or kills its host.

From Slate ● Mar. 29, 2017

The scoutmaster had given them a long lecture about disrupting nature—by the end of it, Jonah felt guilty about how many protozoans he’d probably killed.

From "Found" by Margaret Peterson Haddix