1. Not classified hierarchically
   - nonhierarchical

See also: ungraded, unordered, unranked

• Upanishad
• upas
• upbeat
• upbound
• upbraid
• upbraider
• upbraiding
• upbringing
• upcast
• upchuck
• upcoming
• upcountry
• upcurved
• update
• updating
• updation
• Updike
• updraft
• upend
• upended
• upending
• upfield
• upfront
• upgradation
• upgrade