[ adverb, uhn-der-ground; adjective, noun, verb uhn-der-ground ]
See synonyms for: undergroundundergrounds on Thesaurus.com

  1. beneath the surface of the ground: traveling underground by subway.

  2. in concealment or secrecy; not openly: subversion carried on underground.

  1. existing, situated, operating, or taking place beneath the surface of the ground.

  2. used, or for use, underground.

  1. hidden or secret; not open: underground political activities.

  2. published or produced by political or social radicals or nonconformists: an underground newspaper.

  3. avant-garde; experimental: an underground movie.

  4. critical of or attacking the established society or system: underground opinion.

  5. of or for nonconformists; unusual: an underground vegetarian restaurant.

  1. the place or region beneath the surface of the ground.

  2. an underground space or passage.

  1. a secret organization fighting the established government or occupation forces: He fought in the French underground during the Nazi occupation of France.

  2. (often initial capital letter) a movement or group existing outside the establishment and usually reflecting unorthodox, avant-garde, or radical views.

  3. Chiefly British. a subway system.

verb (used with object)
  1. to place beneath the surface of the ground: to underground utility lines.

Origin of underground

First recorded in 1565–75; under- + ground1

Words Nearby underground

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use underground in a sentence

British Dictionary definitions for underground


  1. occurring, situated, or used below ground level: an underground tunnel; an underground explosion

  2. secret; hidden: underground activities

  1. going below ground level: the tunnel led underground

  2. into hiding or secrecy: the group was driven underground

  1. a space or region below ground level

    • a movement dedicated to overthrowing a government or occupation forces, as in the European countries occupied by the German army in World War II

    • (as modifier): an underground group

  1. the underground an electric passenger railway operated in underground tunnels: US and Canadian equivalent: subway

  2. (usually preceded by the)

    • any avant-garde, experimental, or subversive movement in popular art, films, music, etc

    • (as modifier): the underground press; underground music

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012