n.[theS]

1. （大写）阴间，地狱
2. 下层社会；黑社会
   That quiet man was an underworld king-pin.

   那个安安静静的人是个黑社会老大哥。

   The pot trade is controlled by the underworld.

   毒品生意为黑社会所控制。

3. 【古】地球，大地

n.

1. the world of criminals or of organized crime.
2. the mythical abode of the dead, imagined as being under the earth.