Protozoa

noun
1.
a major grouping or superphylum of the kingdom Protista, comprising the protozoans.
noun, plural protozoans (especially collectively) protozoa
[proh-tuh-zoh-uh] /ˌproʊ təˈzoʊ ə/ (Show IPA)
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.
adjective
2.
of, relating to, or characteristic of a protozoan.
noun, plural protozoa
[proh-tuh-zoh-uh] /ˌproʊ təˈzoʊ ə/ (Show IPA)
1.
protozoan.
noun (pl) -zoa (-ˈzəʊə), -zoans
1.
Also called protozoon (ˌprəʊtəˈzəʊɒn), (pl) -zoa. 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
adjective
2.
of or relating to protozoans

protozoa pro·to·zo·a (prō’tə-zō’ə)
n.
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.
protozoan
(prō’tə-zō’ən)
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.
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.