stroma

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

• noun The connective tissue framework of an organ, gland, or other structure, as distinguished from the tissues performing the special function of the organ or part.
• noun The spongy, colorless framework of a red blood cell or other cell.
• noun The colorless semiliquid material inside a chloroplast, in which the thylakoid membranes are embedded and where the dark reactions of photosynthesis occur.
• noun A dense mass of fungal hyphae on or in which reproductive structures develop.

from The Century Dictionary.

• noun In anatomy: The sustentacular tissue or substance of a part or organ, usually of connective tissue.
• noun In botany: In fungi, a variously shaped more or less continuous layer of cellular tissue, in which perithecia or other organs of fructification are immersed. Sometimes called receptacle. See cut under ergot.
• noun In vegetable physiology, the solid matter remaining after all the fluid has been expressed from protoplasm.

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

• noun The connective tissue or supporting framework of an organ.
• noun The spongy, colorless framework of a red blood corpuscle or other cell.
• noun (Bot.) A layer or mass of cellular tissue, especially that part of the thallus of certain fungi which incloses the perithecia.

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

• noun anatomy the tissue structure of an organ, etc., that serves to support it

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

• noun the dense colorless framework of a chloroplast
• noun a mass of fungal tissue that has spore-bearing structures embedded in it or on it
• noun the supporting tissue of an organ (as opposed to parenchyma)