Three feet
By defintion, a tunnel is underground.
There is no underground tunnel.
it is an adjective because it is describing something.ex. the tunnel is underground-it describes where the tunnel is :)
Aardvarks eat termites and underground fruit. Probably as a source of water.
Sea
The one word synonym for "underground passageway" is "tunnel".
oasis
a tunnel
underground tunnel
From the underground tunnel.
Burrow
Burrow