parenchyma

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

• noun Anatomy The tissue characteristic of an organ, as distinguished from associated connective or supporting tissues.
• noun Botany A simple plant tissue, composed of thin-walled cells and forming the greater part of leaves, roots, the pulp of fruit, and the pith of stems.

from The Century Dictionary.

• noun In anatomy and zoology: The proper tissue or substance of any part or organ, as distinguished from the connective or other sustentacular tissue which it contains.
• noun The undifferentiated body-substance or chyme-mass of the unicellular animal, as an infusorian; indistinguishable cell-substance; endoplasm.
• noun The general substance of the interior of the parenchymatous worms.
• noun In botany, the fundamental cellular tissue of plants: contradistinguished from prosenchyma, or fibrovascular tissue.
• noun Also parenchyme.

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

• noun (Biol.) The soft cellular substance of the tissues of plants and animals, like the pulp of leaves, the soft tissue of glands, and the like.

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

• noun The functional part of an organ, as opposed to supporting tissue.
• noun botany The ground tissue making up most of the non-woody parts of a plant.

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

• noun the primary tissue of higher plants composed of thin-walled cells that remain capable of cell division even when mature; constitutes the greater part of leaves, roots, the pulp of fruits, and the pith of stems
• noun animal tissue that constitutes the essential part of an organ as contrasted with e.g. connective tissue and blood vessels