accretion definition
Full Definition of ACCRETION. 1. : the process of growth or enlargement by a gradual buildup: as a: increase by external addition or accumulation (as by adhesion of external parts or particles) b: the increase of land by the action of natural forces. 2. â acÂ·creÂ·tionÂ·ary \-shÉ-Ëner-Ä, -Ëne-rÄ\ adjective.