| U | Unlimited 
| Others |
| U | Unlocked
| Others |
| U | Unlucky
| Others |
| U | Unmodified
| Others |
| U | Unofficial
| Others |
| U | Unplasticised
| Others |
| U | Unredacted
| Others |
| U | Unreliable
| Others |
| U | Unsatisfactory
| Others |
| U | Unsigned
| Others |
| U | Unterseeboot
| Others |
| U | Unusual
| Others |
| U | Unwind tape
| Others |
| U | Up
| Others |
| U | Upbuilding
| Others |
| U | Update
| Others |
| U | Uphill
| Others |
| U | Upper
| Others |
| U | Upsilon
| Others |
| U | Uracil
| Others |
| U | Uranium
| Element |
| U | Urban
| Others |
| U | Urgent
| Others |
| U | Ursula
| Others |
| U | Use
| Others |
| U | Useless
| Others |
| U | User
| Others |
| U | Userid
| Others |
| U | Users
| Others |
| U | Wind Speed
| Others |
| U | You
| Others |
| U of G | University of Guelph
| Others |
| U OF K | University of Khartoum
| Others |
| U OF MAHDI | University of Elimam Elmahdi
| Others |
| U&A | Usage & Attitudes
| Others |
| U&C | Usual & Customary
| Others |
| U&C | Usual and Customary
| Others |
| U&E | Urea & Electrolites (potassium, sodium, carbon dioxide, and chloride)
| Others |
| U&E | Urea & Electrolytes - blood test
| Others |
| U&E's | Urea and Electrolytes
| Others |
| U&L | Upper And Lower
| Others |
| U&LC | Uppercase and Lowercase
| Others |
| U&LRA | Upper and Lower Radius Arms
| Others |
| U&LW | Upper and Lower Wishbones
| Others |
| U&M | Units & Measurements
| Others |
| U&MNP | Ulnar And Median Nerve Palsy
| Others |
| U&MPV | Utility and Multi Purpose Vehicle
| Others |
| U&P | Username and Password
| Others |
| U&R | Update and Restore
| Others |
| U-ACH | UKC (United Kennel Club) Agility CHampion
| Others |