| Acronym | Definition |
|---|
| U | University |
| U | You |
| U | Upper |
| U | Underlined |
| U | Unsatisfactory |
| U | Und (German: And) |
| U | United |
| U | Ultra |
| U | Universal |
| U | Upper Class |
| U | Wind Speed |
| U | Update(d) (action code) |
| U | Used |
| U | Utility |
| U | Uncle |
| U | Unlimited Time (broadcasting operating schedules) |
| U | Urgent |
| U | Umbrella |
| U | Unit |
| U | Sunday (one letter abbreviation for day of week) |
| U | Unified |
| U | Utah (ammunition headstamp) |
| U | Utility (US military aircraft designation; as in U-6 Beaver) |
| U | Kosher (from Union of Orthodox Hebrew Congregations) |
| U | Uranium |
| U | Uniform (aviation letter code) |
| U | Unclassified |
| U | Unitary (mathematics) |
| U | Umpire |
| U | Atomic Unit (measure of mass) |
| U | Uracil |
| U | Uncleared |
| U | Unsymmetrical |
| U | Umdrehungen (German: RPM) |
| U | Unterseeboot (German: submarine) |
| U | Union Metallic Cartridge Co (division of Remington Arms; used on head stamp of .22 cartridges) |
| U | Envelope or Letter Sheet (Scott Catalogue prefix; philately) |
| U | Unit of measurement for rackmount equipment (U is 1.75in or 4.44cm) |
| U | Unknown Wind Intensity (weather reports) |
| U | US DoT tire speed rating (124 mph) |