- White nervous tissue constituting the conducting portion of the brain and spinal cord.
Definition from: CRISP Thesaurus via Unified Medical Language System at the National Library of Medicine
- Neural tissue especially of the brain and spinal cord that consists largely of myelinated nerve fibers bundled into tracts, has a whitish color, and typically underlies the gray matter.
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
See also Understanding Medical Terminology.