n. The act or operation of rectifying.n. The process of refining a substance by repeated or fractional distillation: it is in this way freed from other substances which are either more or less volatile than itself, or from non-volatile matters: as, tho rectification of spirits. The concentration of sulphuric acid in platinum or glass vessels is sometimes (improperly) called rectification.n. In geometry, the determination of a straight line whose length is equal to a given portion of a curve; the finding a formula for the length of the arc of a given curve.n. In its specific use in relation to the increase of strength of alcoholic liquors by distillation, rectification signifies repeated fractional evaporation of the mixed liquid, dephlegmation repeated fractional condensation of the mixed vapor. Both words are simultaneously applied in the improved forms of still.n. In astral., the ascertainment of the true time of birth by comparison of the directions deduced from the estimated time with the dates of events in the native's life.