Adit \Ad"it\, n. [L. aditus, fr. adire, ?aitum, 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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Tunnel \Tun"nel\, n. . [F. tonnelle a semicircular, wagon-headed vault, a tunnel net, an arbor, OF. also tonnel; dim. of tonne a tun; -- so named from its resemblance to a tun in shape. See Ton.]

1. A vessel with a broad mouth at one end, a pipe or tube at the other, for conveying liquor, fluids, etc., into casks, bottles, or other vessels; a funnel.

2. The opening of a chimney for the passage of smoke; a flue; a funnel.

And one great chimney, whose long tunnel thence The smoke forth threw. --Spenser.

3. An artificial passage or archway for conducting canals or railroads under elevated ground, for the formation of roads under rivers or canals, and the construction of sewers, drains, and the like.

4. (Mining) A level passage driven across the measures, or at right angles to veins which it is desired to reach; -- distinguished from the drift, or gangway, which is led along the vein when reached by the tunnel.

Tunnel head (Metal.), the top of a smelting furnace where the materials are put in.

Tunnel kiln, a limekiln in which coal is burned, as distinguished from a flame kiln, in which wood or peat is used.

Tunnel net, a net with a wide mouth at one end and narrow at the other.

Tunnel pit, Tunnel shaft, a pit or shaft sunk from the top of the ground to the level of a tunnel, for drawing up the earth and stones, for ventilation, lighting, and the like.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Tunnel \Tun"nel\, v. t. [imp. & p. p. Tunneledor Tunnelled; p. pr. & vb. n. Tunneling or Tunnelling.]

1. To form into a tunnel, or funnel, or to form like a tunnel; as, to tunnel fibrous plants into nests. --Derham.

2. To catch in a tunnel net.

3. To make an opening, or a passageway, through or under; as, to tunnel a mountain; to tunnel a river.

Source: Webster's Revised Unabridged Dictionary (1913)