- u ... Ubangi languages
- Ubangi River ... Uchreditelnoye Sobraniye
- uchronia ... Uea
- Ueber die Autonomie der Rabbinen ... uguns mate
- Uh Huh Her ... Ukrainian Catholic Church
- Ukrainian Democratic Alliance for Reform ... Ullathorne, William Bernard
- Ullikummi ... ultimobranchial tissue
- ultimogeniture ... Ulysses
- Ulzana’s Raid ... Umeå IK
- Umehara Ryūzaburō ... Unanimism
- Unanimisme ... undecidability theorem, Turing’s
- undecidable figure ... Understanding, Inc.
- understatement ... Unfinished Symphony
- unfolded protein response ... Unified State Political Administration
- Unified Task Force ... Union for the Presidential Majority
- Union for the Presidential Majority ... unique DNA
- unique factorization theorem ... United Company of Barber Surgeons
- United Company of Merchants of England Trading to the East Indies ... United Nations Fund for Population Activities
- United Nations High Commissioner for Human Rights, Office of the ... United States Army Military District of Washington
- United States Army Signal Corps ... United States presidential election of 1852
- United States presidential election of 1856 ... United States Women’s Amateur Championship
- United States Women’s Bureau ... Universal man
- Universal Men ... unjust enrichment
- unke ... Unseld, Wes
- Unser Schweizer Standpunkt ... Uomini e no
- uomo che andrà in America, L’ ... Upper Atmosphere Research Panel
- Upper Austria ... upsetting
- Upshaw, Dawn ... uranium-234–uranium-238 dating
- uranium-235 ... Urci
- Urd ... Urkhi-Teshub
- URL ... Ursula, Order of Saint
- Ursula, Saint ... USB
- USB flash drive ... USS
- USS Arizona Memorial ... Utah, University of
- Utah/United States Film Festival ... Utricula
- utricular macula ... Uzan, Cem
- Uzan, Cem Cengiz ... Uzziah