pro·​to·​zo·​an ˌprō-tə-ˈzō-ən How to pronounce protozoan (audio)
: any of a phylum or subkingdom (Protozoa) of chiefly motile and heterotrophic unicellular protists (such as amoebas, trypanosomes, sporozoans, and paramecia) that are represented in almost every kind of habitat and include some pathogenic parasites of humans and domestic animals
protozoan adjective

Examples of protozoan in a Sentence

Recent Examples on the Web But once the fish had died, the remaining dinoflagellates started to circle the protozoan. Patrick Huyghe, Discover Magazine, 11 Nov. 2019 Malaria is caused by an infection with one of five protozoan parasites of the Plasmodium genus. Beth Mole, Ars Technica, 27 June 2023 The other five structures possibly represent additional worm eggs or protozoan cysts. Laura Baisas, Popular Science, 9 Aug. 2023 Several more of the round shapes appeared to be worm eggs of an indeterminate type, and the last shape resembled either another worm egg or evidence of a protozoan infection. Matt Hrodey, Discover Magazine, 9 Aug. 2023 Instead, the alga survived and became a symbiotic partner to the protozoan, feeding it the fruits of its photosynthesis. Kevin Hartnett, Quanta Magazine, 6 July 2023 In addition to explaining the cells’ prowess at photosynthesis, the new work helps to confirm the theory that those phytoplankton arose through a symbiotic alliance between a protozoan and a resilient green alga. Kevin Hartnett, Quanta Magazine, 6 July 2023 And now to the protozoan brute of the matter, leishmaniasis. Rebecca Kreston, Discover Magazine, 4 Nov. 2011 This disease is caused by a tiny protozoan the mosquito picks up, and in some areas, mosquitoes are such effective vectors of malaria that 100 percent of them carry the disease. John Sass, Field & Stream, 11 Apr. 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'protozoan.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


New Latin Protozoa, from prot- + -zoa

First Known Use

circa 1864, in the meaning defined above

Time Traveler
The first known use of protozoan was circa 1864

Dictionary Entries Near protozoan

Cite this Entry

“Protozoan.” Dictionary, Merriam-Webster, Accessed 16 Apr. 2024.

Kids Definition


pro·​to·​zo·​an ˌprōt-ə-ˈzō-ən How to pronounce protozoan (audio)
: any of a phylum or group of microorganisms (as amoebas and paramecia) that are single-celled protists and have varied structure and physiology and often complicated life cycles
protozoan adjective

Medical Definition


1 of 2 noun
pro·​to·​zo·​an -ˈzō-ən How to pronounce protozoan (audio)
: any protist of the phylum or subkingdom Protozoa


2 of 2 adjective
: of or relating to the phylum or subkingdom Protozoa

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