Definition of CAUCASIAN. 1. : of or relating to the Caucasus or its inhabitants.2. : of, constituting, or characteristic of a race of humankind native to Europe, North Africa, and southwest Asia and classified according to physical features —used especially in referring to persons of European descent having usually light skin pigmentation.— Caucasian noun.edical Definition of CAUCASIAN. 1. : of or relating to the white race of humankind as classified according to physical features. 2. : of or relating to the white race as defined by law specifically as composed of persons of European, North African, or southwest Asian ancestry. — Caucasian noun.