cortex
cor.tex \'ko.r-.teks\ \'ko.rt-*-.se-z\ n or cor.ti.ces or cor.tex.es [L cortic-, cortex bark] pl 1: a plant bark or rind used medicinally 2: the outer or superficial part of an organ or body structure; esp :: the outer layer of gray matter of the cerebrum and cerebellum 3a: the typically parenchymatous layer of tissue external to the vascular t issue and internal to the corky or epidermal tissues of a green plant; broadly : all tissues external to the xylem 3b: an outer or investing layer of various algae, lichens, or fungi
Webster's English Dictionary