accretion
noun /əˈkriːʃn/
  /əˈkriːʃn/
(specialist or formal)- [countable] a layer of a substance or a piece of matter that is slowly added to something
 - [uncountable] the process of new layers or matter being slowly added to something
- the accretion of sand by wind action
 
 
Word Originearly 17th cent.: from Latin accretio(n-), from accrescere ‘become larger’, from ad- ‘to’ + crescere ‘grow’.