Biology. With capital initial. A class of organisms comprising microscopic forms; protozoa. Obsolete. rare.
With singular agreement: a group of phyla of the kingdom Protista (formerly also treated as a single phylum of the animal kingdom), comprising…
Unicellular animals collectively; protozoa.
a subdivision of the animal kingdom, including the lowest living forms; = Protozoa, n. (New Sydenham Soc. Lexicon 1886).