spinal cord

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

• noun The thick, whitish cord of nerve tissue that extends from the medulla oblongata down through the spinal column and from which the spinal nerves branch off to various parts of the body.

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

• noun anatomy A thick, whitish cord of nerve tissue which is a major part of the vertebrate central nervous system. It extends from the brain stem down through the spine, with nerves branching off to various parts of the body.

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

• noun a major part of the central nervous system which conducts sensory and motor nerve impulses to and from the brain; a long tubelike structure extending from the base of the brain through the vertebral canal to the upper lumbar region