accretionn.[L. accretio, fr. accrescere to increase. Cf. Crescent, Increase, Accrue.]()1. The act of increasing by natural growth; esp. the increase of organic bodies by the internal accession of parts; organic growth.(Arbuthnot.)2. The act of increasing, or the matter added, by an accession of parts externally; an extraneous addition; as, an accretion of earth.()A mineral . . . augments not by growth, but by accretion. (Owen.)To strip off all the subordinate parts of his narrative as a later accretion. (Sir G. C. Lewis.)3. Concretion; coherence of separate particles; as, the accretion of particles so as to form a solid mass.()4. A growing together of parts naturally separate, as of the fingers or toes.(Dana.)5. (Law) The adhering of property to something else, by which the owner of one thing becomes possessed of a right to another; generally, gain of land by the washing up of sand or soil from the sea or a river, or by a gradual recession of the water from the usual watermark.(Wharton. Kent.)