Definition of "adit"

adit

/ˈæ.dɪt/

noun
plural adits
1. A horizontal or nearly horizontal passage from the surface into a mine, as contrasted with a shaft or vertical entry passage. An adit may be used for ventilation, haulage, drainage, or other purposes.
  Quotations
  The Old Mine is currently entered through an upper adit as the main is no longer accessible.
  2006, Mike Hetman, IronMiners.com
  The adit sloped downwards into the bowels of some long-fallen building, following a passage that had silted up when the city had first been buried.
  2008, Iain M. Banks, Matter, page 445