1. Situated, occurring, or operating below the surface of the earth: underground caverns; underground missile sites.
a. Hidden or concealed; clandestine: underground resistance to the tyrant.
b. Of or relating to an organization involved in secret or illegal activity: underground trade in weapons.
3. Of or relating to an avant-garde movement or its films, publications, and art, usually privately produced and of special appeal and often concerned with social or artistic experiment.
1. A clandestine, often nationalist, organization fostering or planning hostile activities against, or the overthrow of, a government in power, such as an occupying military government: "an underground of dissident intellectuals" (Kenneth L. Woodward).
2. Chiefly British A subway system.
3. An avant-garde movement or publication.
1. Below the surface of the earth.
2. In secret; stealthily.
tr.v. un·der·ground·ed, un·der·ground·ing, un·der·grounds
To situate under the ground: workers undergrounding telephone lines.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.