Noun | 1. | white matter - whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths nerve tissue, nervous tissue - tissue composed of neurons fibrous astrocyte - star-shaped cells with long processes; found in the white matter of the brain and spinal cord nerve pathway, nerve tract, pathway, tract - a bundle of myelinated nerve fibers following a path through the brain central nervous system, CNS, systema nervosum centrale - the portion of the vertebrate nervous system consisting of the brain and spinal cord |