n. The act of accreting or accrescing; a growing to; an increase by natural growth; an addition; specifically, an increase by an accession of parts externally.n. In pathology, the growing together of parts normally separate, as the fingers or toes.n. The thing added; an extraneous addition; an accession: commonly used in the plural, and restricted to accessions made slowly and gradually by some external force.n. In law: The increase or growth of property by external accessions, as by alluvium naturally added to land situated on the bank of a river, or on the seashore.n. In Scots law, the completion of an originally defective or imperfect right by some subsequent act on the part of the person from whom the right was derived.n. In forestry, increase in diameter or height: distinguished from increment, increase in volume.n. In petrol., a term proposed by Johnston-Lavis for a mass formed in solution by deposition about a nucleus, as in oölite, or upon the walls of a cavity.