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

See also: covert, subsurface

• unredeemable
• unredeemed
• unreduced
• unreel
• unrefined
• unreflected
• unreflective
• unreformable
• unreformed
• unrefreshed
• unregenerate
• unregenerated
• unregistered
• unregretful
• unregretting
• unregularity
• unregulated
• unrehearsed
• unrejoicing
• unrelated
• unrelatedness
• unrelaxed
• unreleased
• unrelenting
• unrelentingly