Source : Webster's Revised Unabridged Dictionary (1913)

Syncytium \Syn*cy"ti*um\, n.; pl. {Syncitia}. [NL., from Gr. ?
   together + ? a hollow vessel.]
   1. (Biol.) Tissue in which the cell or partition walls are
      wholly wanting and the cell bodies fused together, so that
      the tissue consists of a continuous mass of protoplasm in
      which nuclei are imbedded, as in ordinary striped muscle.

   2. (Zo["o]l.) The ectoderm of a sponge.

Source : WordNet®

syncytium
     n : a mass of cytoplasm containing several nuclei and enclosed
         in a membrane but no internal cell boundaries (as in
         muscle fibers)
     [also: {syncytia} (pl)]