- of or about being under the ground
- Underground water is drying up.
- secret or not well known
- The underground music scene is really interesting.
- Underground drug sales have increased over the last year.
- being or moving under the ground
- Let's go underground. It's safer down there.
- The new trains will run underground.
- If you go underground, you keep your activities secret.
- The underground is a system of trains that runs mostly under the ground.
- The London underground is a great way to move about the city.