a major grouping or superphylum of the kingdom Protista, comprising the protozoans.

1825–35; < Neo-Latin; see proto-, -zoa Unabridged


[proh-tuh-zoh-uhn] Biology.
noun, plural protozoans (especially collectively) protozoa [proh-tuh-zoh-uh] .
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.
of, pertaining to, or characteristic of a protozoan.

1860–65; Protozo(a) + -an


[proh-tuh-zoh-on, -uhn]
noun, plural protozoa [proh-tuh-zoh-uh] .

singular of Protozoa Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
protozoan (ˌprəʊtəˈzəʊən)
n , pl -zoa, -zoans, -zoa
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
2.  of or relating to protozoans
[C19: via New Latin from Greek proto- + zoion animal]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1834, from Mod.L., coined 1818 by Ger. zoologist Georg August Goldfuss (1782-1848) from Gk. protos "first" + zoia, pl. of zoion "animal" (see zoo).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

protozoa pro·to·zo·a (prō'tə-zō'ə)
Plural of protozoan.

protozoan pro·to·zo·an (prō'tə-zō'ən) or pro·to·zo·on (-ŏn')
n. pl. pro·to·zo·a (-zō'ə) or pro·to·zo·ans or pro·to·zo·a or pro·to·zo·ons
Any of a group of single-celled, usually microscopic, eukaryotic organisms, such as amoebas, ciliates, flagellates, and sporozoans.

pro'to·zo'an or pro'to·zo'al or pro'to·zo'ic adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
protozoan   (prō'tə-zō'ən)  Pronunciation Key 
Plural protozoans or protozoa
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. See more at protist.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
protozoa [(proh-tuh-zoh-uh)]

Single-celled animals, such as amoebas, that are the most primitive form of animal life. In modern biology, they are classified in the kingdom of Protoctista rather than in the animal kingdom. (See Linnean classification.)

Note: Some protozoa are parasites and may be pathogenic, causing diseases such as malaria and dysentery.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences for protozoa
They are distinguished from protozoa in that they are photosynthetic.
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