noun
: a liquid comparable to serum but containing less dissolved material and in health no floating cells that is secreted from the blood into the lateral ventricles of the brain by the choroid plexus, circulates through the ventricles to the spaces between the meninges about the brain and spinal cord, and is resorbed into the blood through the subarachnoid sinuses, serving chiefly to maintain uniform pressure within the brain and spinal cord but also assisting in the metabolic exchanges