Definition of Epi-

Epi-: Prefix taken from the Greek that means "on, upon, at, by, near, over, on top of, toward, against, among." As in epicanthal fold (a fold of skin that comes down across the inner angle, the canthus, of the eye; epicardium (a layer of fibrous tissue that surrounds the heart and the roots of the great blood vessels); episclera (a thin membrane on top of the sclera, the white of the eye); epidural anesthetic (an anesthetic injected into the epidural space surrounding the fluid-filled sac, called the dura, around the spine which partially numbs the abdomen and legs); etc.