1. Being or operating under the surface of the earth
   "subterranean passages"
   - subterraneous 
2. Lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed)
   "subterranean motives for murder"
   - subterraneous, ulterior

See also: covert, subsurface

Encyclopedia: Subterranean

• National Institute of Justice
• National Institute of Standards and Technology
• National Institutes of Health
• national insurance
• National Intelligence Community
• National Labor Relations Board
• national leader
• National Liberation Army
• National Liberation Front of Corsica
• National Library of Medicine
• national monument
• National Oceanic and Atmospheric Administration
• national park
• National Park Service
• National Reconnaissance Office
• National Rifle Association
• National Science Foundation
• National Security Agency
• National Security Council
• national service
• national socialism
• national socialist
• National Socialist German Workers' Party
• National Technical Information Service
• national trading policy