n. A unicellular organism; a simple unit of aggregation of the first order, as an individual protozoan, or a cell considered with reference to its developmental or evolutionary potentiality.n. In botany, one of the variously shaped proteid bodies, such as chlorophyl-granules, leucoplastids, chromoplastids, etc., which may be clearly differentiated in the protoplasm of active cells.n. They have substantially the same chemical and, with the exception of color, the same physical properties as protoplasm. They are regarded as being the centers of chemical activity in cells.Having the character or quality of a plastid; plastic or plasmic.n. A general name for any permanent organ of the cell except the nucleus and centrosome.