tun·nel 
(tŭnəl)
(tŭnəl)n.
1. An underground or underwater passage.
2. A passage through or under a barrier such as a mountain.
3. A tube-shaped structure.
v. tun·neled, tun·nel·ing, tun·nels or tun·nelled or tun·nel·ling
v.tr.
1. To make a tunnel through or under: tunneling the granite.
2. To produce, shape, or dig in the form of a tunnel: tunnel a passageway out of prison.
v.intr.
To make a tunnel.
[Middle English tonel, barrel, tubular net, from Old French tonnel, diminutive of tonne, tun, possibly of Celtic origin.]
tunnel·er, tunnel·ler n.
tunnel