Adit, n.
Etymology: [L. aditus, fr. adire, , to go to; ad + ire to go.]
1. An entrance or passage. Specifically: The nearly horizontal opening by which a mine is entered, or by which water and ores are carried away; -- called also drift and tunnel.
2. Admission; approach; access. [R.] Yourself and yours shall have Free adit. Tennyson.
Shades of meaning
Fernald has no entry of its own for adit; he lists it under entrance.
He lists it without comment; the entries above explain its neighbors.