Subway
The Underground, The Tube, The Metro
noun
The ground below iron is iron under the ground. It isn't a deposit of iron, though. It's man-made. And what's made of iron? Trains. In this case, because it's underground, it's a subway. Depending on where you live, you might call it the Underground, the Tube, or the Metro
ちかてつ
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
地下鉄に乗って行きます。
I’ll go on the subway.
東京の地下鉄はかなりふくざつです。
Tokyo's subway is extremely complex.
ああ、よかった！地下鉄に乗り遅れちゃうかと思ったよ。
What a relief! I thought I missed the subway train.