The Collaborative International Dictionary of English v.0.48:

Plasmodium \Plas*mo"di*um\, n.; pl. Plasmodia. [NL. See
   Plasma.]
   1. (Biol.) A jellylike mass of free protoplasm, without any
      union of am[oe]boid cells, and endowed with life and power
      of motion.
      [1913 Webster]

   2. (Zool.) A naked mobile mass of protoplasm, formed by the
      union of several am[oe]balike young, and constituting one
      of the stages in the life cycle of Mycetozoa and other low
      organisms.
      [1913 Webster]
      [1913 Webster]

WordNet (r) 3.0 (2006):

plasmodium
    n 1: multinucleate sheet of cytoplasm characteristic of some
         stages of such organisms as slime molds
    2: parasitic protozoan of the genus Plasmodium that causes
       malaria in humans [syn: plasmodium, Plasmodium vivax,
       malaria parasite]