The act of a sovereign in renouncing and relinquishing his government or throne, so that either the throne is left entirely vacant, or is filled by a successor appointed or elected beforehand. Also, where a magistrate or person in office voluntarily renounces or gives it up before the time of service has expired. It differs from resignation, in that resignation is made by one who has received his office from another and restores it into his hands, as an inferior into the hands of a superior; abdication is the relinquishment of an office which has devolved by act of law. It is said to be a renunciation, quitting, and relinquishing, so as to have nothing further to do with a thing, or the doing of such actions as are inconsistent with the holding of it. Chambers.
Law Dictionary – Alternative Legal Definition
government. 1. A simple renunciation of an office, generally understood of a supreme office. James II. of England; Charles V. of Germany; and Christiana, Queen of Sweden, are said to have abdicated. When James III of England left the kingdom, the Commons voted that he had abdicated the government, and that thereby the throne had become vacant. The House of Lords preferred the word deserted, but the Commons thought it not comprehensive enough, for then, the king might have the liberty of returning. 2. When inferior magistrates decline or surrender their offices, they are said to make a resignation.