The Collaborative International Dictionary of English v.0.48:

Protista \Pro*tis"ta\, n. pl. [NL., fr. Gr. prw`tistos first.]
   (Zool.)
   A provisional group in which are placed a number of low
   microscopic organisms of doubtful nature. Some are probably
   plants, others animals.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Protiston \Pro*tis"ton\, n.; pl. Protista. [NL.] (Zool.)
   One of the Protista.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Protista
    n 1: eukaryotic one-celled living organisms distinct from
         multicellular plants and animals: protozoa, slime molds,
         and eukaryotic algae [syn: Protista, division Protista]