1. Incapable of being perceived or known
   - incognoscible, incognisable [Brit]

See also: imperceptible, unperceivable

• undeniable
• undeniably
• undenominational
• undependability
• undependable
• undependableness
• undependably
• undepicted
• under
• under a cloud
• under arms
• under attack
• under fire
• under it
• under that
• under the circumstances
• under the weather
• under wraps
• under-represent
• under-the-counter
• under-the-table
• underachieve
• underachievement
• underachiever
• underact