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a. Growth or increase in size by gradual external addition, fusion, or inclusion.
b. Something contributing to such growth or increase: "the accretions of paint that had buried the door's details like snow" (Christopher Andreae).
2. Biology The growing together or adherence of parts that are normally separate.
a. Slow addition to land by deposition of water-borne sediment.
b. An increase of land along the shores of a body of water, as by alluvial deposit.
4. Astronomy An increase in the mass of a celestial object by its gravitational capture of surrounding interstellar material.
[Latin accrētiō, accrētiōn-, from accrētus, past participle of accrēscere, to grow; see accrue.]
ac·cre′tion·ar′y (-shə-nĕr′ē), ac·cre′tive adj.