From The Collaborative International Dictionary of English v.0.48:
accretion \ac*cre"tion\ ([a^]k*kr[=e]"sh[u^]n), n. [L. accretio,
fr. accrescere to increase. Cf. Crescent, Increase,
Accrue.]
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1. The act of increasing by natural growth; esp. the increase
of organic bodies by the internal accession of parts;
organic growth. --Arbuthnot.
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2. The act of increasing, or the matter added, by an
accession of parts externally; an extraneous addition; as,
an accretion of earth.
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A mineral . . . augments not by growth, but by
accretion. --Owen.
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To strip off all the subordinate parts of his
narrative as a later accretion. --Sir G. C.
Lewis.
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3. Concretion; coherence of separate particles; as, the
accretion of particles so as to form a solid mass.
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4. A growing together of parts naturally separate, as of the
fingers or toes. --Dana.
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5. (Law)
(a) 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.
(b) Gain to an heir or legatee, by failure of a coheir to
the same succession, or a co-legatee of the same
thing, to take his share. --Wharton. Kent.
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