adj.
1.under the level of the ground
2.conducted with or marked by hidden aims or methods
3.used of independent armed resistance forces underground adv.
1.in or into hiding or secret operation
2.beneath the surface of the earth underground n.
1.a secret group organized to overthrow a government or occupation force
2.electric underground railway
Idiom of the Day
live down (something)
to remove blame or distrust by good conduct, to cause something to be forgiven by not repeating it
Our supervisor is trying to live down his reputation of being a difficult person to work for.