(1) The restoration, by surgical or manipulative procedures, of a part to its normal anatomic relation. SYN: repositioning (2). (2) In chemistry, a reaction involving a gain of one or more electrons by a substance, such as when iron passes from the ferric (3+) to the ferrous (2+) state, or when hydrogen is added to the double bond of an organic compound, or when an aldehyde is converted to an alcohol. [L. reductio, fr. re-duco, pp. ductus, to lead back]