Source : Webster's Revised Unabridged Dictionary (1913)

Plastid \Plas"tid\, Plastide \Plas"tide\, n. [Gr. ?, ?, a
   creator.]
   1. (Biol.) A formative particle of albuminous matter; a
      monad; a cytode. See the Note under {Morphon}. --Haeckel.

   2. (Bot.) One of the many minute granules found in the
      protoplasm of vegetable cells. They are divided by their
      colors into three classes, chloroplastids, chromoplastids,
      and leucoplastids.

Source : WordNet®

plastid
     n : any of various small particles in the cytoplasm of the cells
         of plants and some animals containing pigments or starch
         or oil or protein