underground

underground, subway, tube

这些名词均可表示“地铁”之意。
underground: 一般用词，指城市中的地铁，主要用于英国。
subway: 指城市中的地铁或通道，主要用于美国。
tube: 主要用于英国口语中。

名词 underground:

1. a secret group organized to overthrow a government or occupation force
   同义词：resistance
2. an electric railway operating below the surface of the ground (usually in a city)
   同义词：metro, tube, subway system, subway

形容词 underground:

1. under the level of the ground
   同义词：belowground
2. conducted with or marked by hidden aims or methods
   同义词：clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover

副词 underground:

1. in or into hiding or secret operation
2. beneath the surface of the earth

1. The cavers discovered a vast underground chamber.
   探穴人发现了一个地下大洞穴。
2. The revolutionist eluded capture for weeks by hiding underground.
   那位革命者为避免被捕在地下躲藏了几个星期。
3. The missile is delivered from underground.
   这种导弹由地下发射。
4. Some miners were trapped underground after the collapse.
   塌方后，有些矿工被困在地下。
5. The prisoner escaped by digging an underground tunnel.
   囚犯挖了一条地道逃跑了。
6. The spy never told his family about his underground activities.
   这位间谍从未把他的秘密活动告诉家里人。
7. There is an underground car park near the supermarket.
   这个超市附近有一个地下停车场。