Underground (Noun)
Meaning 1
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'".
Classification
Nouns denoting man-made objects.
Synonyms
Hypernyms
Meaning 2
A secret group organized to overthrow a government or occupation force.
Classification
Nouns denoting groupings of people or objects.