The Columbia Encyclopedia, Sixth Edition. 2001-07.
adit
(d´t) (KEY) , in mining, underground passage excavated nearly horizontally, with one end open to the earths surface, usually used to service a mine. The adit end is the furthermost end from the surface, i.e., the location where miners work. The adit collar is the area where an adit opens to the surface and must be reinforced against any surface weakness.