Protozoa

n. any eukaryotic organism (usually single-celled) from the kingdom Protista

n. phylum comprised of the protozoans, phylum comprised of eukaryotic organisms (usually single-celled) from the kingdom Protista

Protozoa (in Greek proto = first and zoa = animals) are one-celled eukaryotes (that is, unicellular microbes whose cells have membrane-bound nuclei) that commonly show characteristics usually associated with animals,  mobility and heterotrophy. Protozoans were commonly grouped in the kingdom Protista together with the plant-like algae and fungus-like water molds and slime molds. In 21st-century systematics, however, most of the algae are classified in kingdoms such as Plantae and Chromista; and in such cases the remaining life forms are occasionally classified as a kingdom Protozoa. But the name is misleading, since protozoans are neither Animalia nor Metazoa, with the possible exception of the enigmatic, moldy Myxozoa).
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Noun
1. in some classifications considered a superphylum or a subkingdom; comprises flagellates; ciliates; sporozoans; amoebas; foraminifers
(synonym) phylum Protozoa
(hypernym) phylum
(member-holonym) Protoctista, kingdom Protoctista
(member-meronym) protozoan, protozoon

n. protozoan, any eukaryotic organism (usually single-celled) from the kingdom Protista

(pl. )
of Protozoon
  

(n. pl.)
The lowest of the grand divisions of the animal kingdom.