Množina: adits

ETYM Latin aditus, from adire, aitum, to go to; ad + ire to go.
A nearly horizontal passage from the surface into a mine.
Opening or passage into a mine.
Entrance, especially horizontal passage into mine.
In mining, a horizontal shaft from the surface to reach the mineral seam. It was a common method of mining in hilly districts, and was also used to drain water. The mineral-bearing rock is excavated by digging horizontally into the side of a valley. It is used, for example, in coal mining.