defile, narrow, obstruction

隘 is composed of the radical of 阜 (mound) and 益 (benefit). 阜 refers to hills or mountainous terrain, while 益 visually depicts water overflowing from a container, carrying the meaning of being filled to capacity. When an area is filled with mountains, hazardous obstacles abound and passages become restricted, so 隘 associationally conveys a narrow pass, bottleneck, or obstruction.