Толковый словарь английского языка Oxford English Reference - equation

n. 1 the process of equating or making equal; the state of being equal. 2 Math. a statement that two mathematical expressions are equal (indicated by the sign =). 3 Chem. a formula indicating a chemical reaction by means of symbols for the elements taking part. Phrases and idioms equation of the first order, second order , etc. an equation involving only the first derivative, second derivative, etc. Derivatives equational adj. Etymology: ME f. OF equation or L aequatio (as EQUATE)