Subterranean

Pronunciation: /səbtərˈeɪniːən/

Subterranean (adjective)

  1. Located or happening below the surface of the ground.
  2. Secret or hidden from view, not easily seen or known.

Examples

  • The subterranean tunnel stretched for miles.
  • Subterranean caves can be home to unique wildlife.

Common collocations: subterranean tunnel, subterranean cave, subterranean network, subterranean agenda, subterranean motives