The word "函谷关" is formed by combining three characters: "函" meaning a box or enclosed area, which describes the narrow, box-like topography of the location; "谷" meaning valley, indicating the geographical feature; and "关" meaning a strategic pass or gate, specifying its function as a fortified entry point. Together, they literally denote a pass situated in a valley with a box-shaped formation, thus creating the name for this specific historical site.