barium enema: enema in which a contrast medium (usually barium sulfate) is injected into the rectum and X-rays are taken to search for lesions
enema: an injection of a liquid through the anus to stimulate evacuation; sometimes used for diagnostic purposes
equilibrium law: (chemistry) the principle that (at chemical equilibrium) in a reversible reaction the ratio of the rate of the forward reaction to the rate of the reverse reaction is a constant for that reaction