- untrue
- unwritten
- unit
- unit of measurement
- ununquadium
- ununhexium
- ununpentium
- ununtrium
- unnilquadium
- ununbium
- Uuq
- Uup
- Uut
- Unq
- unmarried woman
- undecaying
- unearth
- unveil
- unfold
- unsound
- unwoven
- unwrapped
- undulate
- uniquely
- up to the hilt
- undefinable
- undefined record
- united mexican states
- underclassman
- underclass
- uveitis
- ulitis
- ureteritis
- uproarious
- underivative
- unplaced
- unmerciful
- unmercifully
- underground press
- upland
- upland rice
- undercover work
- undiplomatic
- understood
- urorectal pouch
- untalented
- unsay
- unwind
- unturned
- unit operation