under the surface of the ground; acting secretly (especially of a movement for resisting the enemy); in, to, a secret place, situation
below the surface
Cases of word usage
1) a kind of dark-grey furry animal living underground and going about at night (badger)
2) a series of underground galleries for the burial of the dead (as in ancient Rome) (catacombs)
3) an underground room for storing coal, wine etc (cellar)
4) (a usually covered) hole, pit or underground tank into which drains (especially for sewage) empty (cesspit)
5) an underground room of a church (crypt)
6) a dark underground cell used (in history) as a prison (dungeon)
7) a room or building for the display of works of art; a horizontal underground passage in a mine (gallery)
8) an underground spring sending out hot water or steam (geyser)
9) (any of many kinds of) liquid which does not mix with water, obtained from animals e.g. cod-liver oil), plants (olive oil), or found underground (petroleum) (oil)
10) a kind of nut growing underground in pairs in a thin shell; a small amount of money (peanut)