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.