Source : Webster's Revised Unabridged Dictionary (1913)

Protozoon \Pro`to*zo"["o]n\ (-[o^]n), n.; pl. {Protozoa}. [NL.]
   (Zo["o]l.)
      (a) One of the Protozoa.
      (b) A single zooid of a compound protozoan.

Protozoa \Pro`to*zo"a\, n. pl. [NL., fr. Gr. ? first + ? an
   animal.] (Zo["o]l.)
   The lowest of the grand divisions of the animal kingdom.

   Note: The entire animal consists of a single cell which is
         variously modified; but in many species a number of
         these simple zooids are united together so as to form a
         compound body or organism, as in the Foraminifera and
         Vorticell[ae]. The reproduction takes place by fission,
         or by the breaking up of the contents of the body after
         encystment, each portion becoming a distinct animal, or
         in other ways, but never by true eggs. The principal
         divisions are Rhizopoda, Gregarin[ae], and Infusoria.
         See also {Foraminifera}, {Heliozoa}, {Protoplasta},
         {Radiolaria}, {Flagellata}, {Ciliata}.

Source : WordNet®

Protozoa
     n : in some classifications considered a superphylum or a
         subkingdom; comprises flagellates; ciliates; sporozoans;
         amoebas; foraminifers [syn: {phylum Protozoa}]