equilibrium /ē′kwilib″rē·əm/ [L, aequilibrium] , 1. a state of balance or rest resulting from the equal action of opposing forces such as calcium and phosphorus in the body. 2. (in psychiatry) a state of mental or emotional balance. 3. (in radiotherapy) a point at which the rate of production of a daughter element is equal to the rate of decay of the parent element and the activities of parent and daughter are identical.
