thalamus

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

• noun A large ovoid mass of gray matter situated in the posterior part of the forebrain that relays sensory impulses to the cerebral cortex.

from The Century Dictionary.

• noun In Gr. archæol., an inner or private room; a chamber; especially, the women's apartment (Homeric); a sekos.
• noun In anatomy: The apparent origin of a cranial nerve; the place where a nerve emerges from or leaves the brain.
• noun Specifically, the optic thalamus; the thalamus of the optic nerve; the great posterior ganglion of the cerebrum, forming the lateral wall of the cerebral ventricle, and connected with its fellow by the middle commissure of the brain. See cut under cerebral.
• noun In botany: The receptacle or torus.
• noun Same as thallus.

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

• noun (Anat.) A mass of nervous matter on either side of the third ventricle of the brain; -- called also optic thalamus.
• noun Same as Thallus.
• noun The receptacle of a flower; a torus.

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

• noun anatomy Either of two large, ovoid structures of grey matter within the forebrain that relay sensory impulses to the cerebral cortex.
• noun botany The receptacle of a flower; a torus.
• noun A thallus.

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

• noun large egg-shaped structures of grey matter that form the dorsal subdivision of the diencephalon