The thoracic diaphragm is a muscle tissue separating the thorax and abdomen of a man. In "Somun(素問)", Gyeok(?) means diaphragm. Its meaning comes from Gyeok(?), a tripod boiler with three separated parts for cooking. In "Yeongchu", Gyeok(膈) is a pictophonetic character which takes the place of Gyeok(?). The different uses of the two words probably does not come from the original writing, but result from longtime transformation.