root canal

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

• noun A pulp-filled channel in a root of a tooth.
• noun A treatment in which diseased tissue from this part of the tooth is removed and the resulting cavity is filled with an inert material.

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

• noun The hollow part of the root of a tooth containing the nerve and blood vessels.
• noun dentistry A surgical operation on a root canal, typically filling it with gutta-percha.

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

• noun the passage in the root of a tooth through which its nerve and blood vessels enter the pulp cavity