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
figure out (someone or something) or figure (someone or something) out
to try to understand someone or something, to solve something
I finally figured out how to use the new DVD recorder.