(noun, adjective, verb, adverb)


1. under the level of the ground

- underground caverns

Similar word(s): subsurface, belowground

2. conducted with or marked by hidden aims or methods

- underground resistance

Similar word(s): covert, clandestine, secret, surreptitious, undercover

Sentences with underground as an adjective:

- There is an underground tunnel that takes you across the river.

- These criminals operate through an underground network.


1. in or into hiding or secret operation

- the organization was driven underground

2. beneath the surface of the earth

- water flowing underground

Sentences with underground as an adverb:

- The tunnel goes underground at this point.


1. a secret group organized to overthrow a government or occupation force

Similar word(s): resistance

Definition categories: group

2. an electric railway operating below the surface of the ground (usually in a city)

- in Paris the subway system is called the `metro' and in London it is called the `tube' or the `underground'

Similar word(s): metro, subway, tube

Definition categories: man–made, railroad, railway


1. To route electricity distribution cables underground