n. A coming, as into the possession of a right or station; attainment; entrance; induction: as, the accession of the people to political power, or to the ballot; accession to an estate, or to the throne.n. The act of acceding, as by assent or agreement; consent; junction; adhesion: as, accession to a demand or proposal; their accession to the party or confederacy was a great gain.n. Increase by something added; that which is added; augmentation; addition: as, an accession of wealth, territory, or numbers.n. In law, a mode of acquiring property, by which the owner of a corporeal substance which receives an addition by growth or by the application of labor has a right to the thing added or to the improvement, as an addition to a house made by a tenant under an ordinary lease.n. In medicine, the attack, approach, or commencement of a disease; access.n. In the election of a pope, the transference of votes from one candidate to another, when the scrutiny has not resulted in a choice. The opportunity of doing this is called an accessit (which see).n. Increase, addition, increment, extension, augmentation.To enter in the accession-book of a library. See accession-book.