noun Any of the eukaryotic, usually unicellular organisms—including protozoans, slime molds and some algae—historically grouped into the kingdom Protista (or Protoctista), now distributed over several clades; any eukaryote that is not a plant, animal or fungus.
noun Any single-celled eukaryote, prokaryote or sponge .mw-parser-output .defdate{font-size:smaller}.