白はく質しつはくしつMeanings1nounwhite matter; substantia albaanatomyAnatomical term referring to the pale-colored tissue in the brain and spinal cord, composed mainly of myelinated nerve fibers.脳のうの白はく質しつは主おもに有ゆう髄ずい神しん経けい線せん維いからなる。The brain's white matter consists mainly of myelinated nerve fibers.