Biol. 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
Any of a group of eukaryotic organisms belonging to the kingdom Protista according to some widely used modern taxonomic systems. The protists include a variety of unicellular, coenocytic, colonial, and multicellular organisms, such as the protozoans, slime molds, brown algae, and red algae.
A unicellular protoctist in taxonomic systems in which the protoctists are considered to form a kingdom.