Accretion

noun

1. The act of increasing by natural growth; especially the increase of organic bodies by the internal accession of parts; organic growth.
2. The act of increasing, or the matter added, by an accession of parts externally; an extraneous addition

   "A mineral ... augments not by growth, but by accretion."

3. Something added externally to promote growth the external growth of an item.
4. Concretion; coherence of separate particles

   "the accretion of particles so as to form a solid mass"

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