1. A making equal; equal division; equality; equilibrium. Again the golden day resumed its right, And ruled in just equation with the night. (Rowe)
2. (Science: mathematics) An expression of the condition of equality between two algebraic quantities or sets of quantities, the sign = being placed between them; as, a binomial equation; a quadratic equation; an algebraic equation; a transcendental equation; an exponential equation; a logarithmic equation; a differential equation, etc.
3. (Science: astronomy) a quantity to be applied in computing the mean place or other element of a celestial body; that is, any one of the several quantities to be added to, or taken from, its position as calculated on the hypothesis of a mean uniform motion, in order to find its true position as resulting from its actual and unequal motion.
4. Equation box, or Equational box, a system of differential gearing used in spinning machines for regulating the twist of the yarn. It resembles gearing used in equation clocks for showing apparent time.
5. (Science: astronomy) equation of the center, the difference between the place of a planet as supposed to move uniformly in a circle, and its place as moving in an ellipse.
Origin: L. Aequatio an equalizing: cf. F. Equation equation. See Equate.