Real Dictionary

protist in American English
in some systems of classification, any of a kingdom (Protista) of one-celled organisms, as algae, yeasts, or protozoans, having characteristics found in both plants and animals
noun: any of various one-celled organisms, classified in the kingdom Protista, that are either free-living or aggregated into simple colonies and that have diverse reproductive and nutritional modes, including the protozoans, eukaryotic algae, and slime molds:

protist in British English
noun: (in some classification systems) any organism belonging to the kingdom Protista, originally including bacteria, protozoans, algae, and fungi, regarded as distinct from plants and animals. It was later restricted to protozoans, unicellular algae, and simpl