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.

Source : WordNet®

protozoon
     n : any of diverse minute acellular or unicellular organisms
         usually nonphotosynthetic [syn: {protozoan}]