plastid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several cytoplasmic organelles, such as chloroplasts, that contain genetic material, have a double membrane, and are often pigmented. Plastids are found in plants, algae, and certain other eukaryotic organisms and have various physiological functions, such as the synthesis and storage of food.

from The Century Dictionary.

• noun A general name for any permanent organ of the cell except the nucleus and centrosome.
• noun 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.
• noun 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.
• noun 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.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Biol.), Archaic A formative particle of albuminous matter; a monad; a cytode. See the Note under morphon.
• noun (Bot.) any of several types of minute granules found in the protoplasm of vegetable cells, having their own membrane, robosomes, and DNA. Among plant cells the most common are chloroplasts, which contain the chlorophyll and the photosynthetic machinery of the cell. They are divided by their colors into three classes, chloroplastids, chromoplastids, and leucoplastids.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology Any of various organelles found in the cells of plants and algae, often concerned with photosynthesis

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various small particles in the cytoplasm of the cells of plants and some animals containing pigments or starch or oil or protein