supervise, inspect

監 is composed of 臣(the picture of a big and popped eye), 人(a man's body) and 皿(a basin which is usually used for holding water). 監 depicts someone staring at the basin, before the invention of mirror, ancient Chinese used the basin of water to reflect their own images, so 監 also meant mirror in the past, but such meaning was then replaced by 鑑, now 監 solely means looking at something intensely.