subway
- underground - metro
‘subway’
A subway is a path for pedestrians under a busy road.
You feel worried if you walk through a subway.
In some American cities, the subway is a railway system in which electric trains travel below the ground in tunnels. In other cities this is called the metro.
I don't ride the subway at night.
You can take the metro to the Smithsonian museums.
‘underground’
Some speakers of British English also use subway to refer to a British railway system like this, but the London and Glasgow systems are usually called the underground. The London system is also called the tube.
He crossed London by underground.
You can take the tube to Green Park and then walk.