accretion vs addendum

accretion

noun
  • The act of increasing, or the matter added, by an accession of parts externally; an extraneous addition. 

  • Gain to an heir or legatee; failure of a coheir to the same succession, or a co-legatee of the same thing, to take his share percentage. 

  • The formation of planets and other bodies by collection of material through gravity. 

  • The gradual increase of land by deposition of water-borne sediment. 

  • Something added externally to promote the external growth of an item. 

  • A growing together of parts naturally separate, as of the fingers or toes. 

  • Concretion; coherence of separate particles. 

  • The act of increasing by natural growth; especially the increase of organic bodies by the internal accession of parts; organic growth. 

  • 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 sail from the sea or a river, or by a gradual recession of the water from the usual watermark. 

addendum

noun
  • Something to be added; especially text added as an appendix or supplement to a document. 

  • The height by which the tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line. 

  • A postscript. 

How often have the words accretion and addendum occurred in a corpus of books? (source: Google Ngram Viewer )