| Ulugh Beg Observatory | Ululation | Ulva |
| Ulva costata | Ulva cuneata | Ulva cylindrica |
| Ulva digitata | Ulva lactuca | Ulva purpurascens |
| Ulva umbilicata | Ulvaceae | Ulvales |
| Ulvina | Ulvophyceae | Ulyanovsk |
| Ulysses (spacecraft) | Ulysses S. Grant | Ulysses, Kansas |
| Ulysses, Nebraska | UM Airlines | Uma |
| Uma Thurman | Umaga (wrestler) | Umar |
| Umar al-Tilmisani | Umar Farouk Abdulmutallab | Umar Khan |
| Umar Muhayshi | Umar Sulaiman Al-Ashqar | Umaru Musa Yar'Adua |
| Umatilla, Florida | Umayyad | Umayyad architecture |
| Umayyad Caliphate | Umayyad Empire | Umayyad invasion of Gaul |
| Umayyad Mosque | Umayyads | Umber View Heights, Missouri |
| Umberto Caligaris | Umberto Eco | Umberto Rizzitano |
| Umbilical artery | Umbilical cord | Umbilical plane |
| Umbilical vein | Umbilical vesicle | Umbiliceae |
| Umbilicus | Umbilicus botryoides | Umbilicus chloranthus |
| Umbilicus citrinus | Umbilicus erectus | Umbilicus giganteus |
| Umbilicus heylandianus | Umbilicus horizontalis | Umbilicus intermedius |
| Umbilicus luteus | Umbilicus parviflorus | Umbilicus rupestris |
| Umbilicus samium | Umbilicus simplex | Umbilicus tropaeolifolius |
| Umbrella | Umbrella term | Umbria |
| UMD | UML | UML Model |
| UML Model diagram | Umm al-Fahm | Umm al-Qura Mosque |
| Umm Nidal | Umma Party (Egypt) | Ummahfilms |
| Umniah | Umrah | UMTS Terrestrial Radio Access Network |
| UMTS المراجعة 8 | Umurbek Bazarbayev | Umut Bulut |
| UN | Un Certain Regard | UN Commission on Human Rights |
| Un drame au Mexique | Un gallo con muchos huevos | Un homme et une femme |
| UN number | Un Paso Adelante (TV series) | UN Peacemaker |
| UN Women | UN-Water | Unaccompanied minor |
| Unadilla (village), New York | Unadilla Township, Michigan | Unadilla, Georgia |
| Unadilla, Nebraska | Unai Alba | Unai Emery |
| Unai Expósito | UNAIDS | Unalakleet, Alaska |
| Unalaska, Alaska | UNAM | Unary operation |
| Unas | UNASUR | Unbalanced line |
| Unbarred spiral galaxy | Unbreakable | Unbreakable (film) |
| Uncaria tomentosa | Uncertainty | Uncertainty principle |
| Uncharted | Uncharted 2: Among Thieves | Uncharted 3: Drake's Deception |
| Uncharted 4: A Thief's End | Uncharted: Drake's Fortune | Uncharted: Golden Abyss |
| Uncia uncia | Uncinaria | Uncinaria hamiltoni |
| Uncinaria rauschi | Uncinaria sanguinis | Uncinaria stenocephala |
| Uncinaria yukonensis | Uncinate process of ethmoid bone | Uncinate process of vertebra |
| Uncle Grandpa | Uncle Sam | Uncombable hair syndrome |
| Unconditional surrender | Unconscious mind | Unconsciousness |
| Uncontrolled airspace | Unconventional computing | Uncoupling (neuropsychopharmacology) |
| Uncus | Uncyclopedia | Undaria pinnatifida |
| Undecane | Undecylenic acid | Under Ash |
| Under Siege (2005 video game) | Under the Bombs | Underarm hair |
| Underconsumption | Underemployment | Undergarment |
| Undergraduate | Undergraduate education | Underhill, Vermont |
| Underhill, Wisconsin | Undernet | Understanding |
| Underwater photography | Underwater search and recovery | Underwood's septa |
| Underwood, Iowa | Underwood, Minnesota | Underwood, North Dakota |
| Underworld (1927 film) | Underworld: Awakening | Underworld: Evolution |
| Underwriting | Undifferentiated connective tissue disease | Undistributed profits |
| Undulatory theory of light | Undulatus asperatus | Unearthed: Trail of Ibn Battuta |
| Uneasy Listening Vol. 1 | Uneasy Listening Vol. 2 | Uneasy Listening, Vol. 1 |
| Uneasy Listening, Vol. 2 | Unemployment | Unemployment benefits |
| Unequal leg length | UNESCO | UNESCO World Heritage Centre |
| Unexpected hanging paradox | Unexploded ordnance | Unfaithful (2002 film) |
| UNFCCC | Unfinished Portrait (novel) | Unfolded protein response |
| Unforgiven | Unfriended | Unger model |
| Ungli | Ungulata | UNI |
| Unión General de Trabajadores | Unica Zürn | Unicameralism |
| Unicast | Unicef | UNICEF |
| Unicode | Unicode anomaly | Unicode block |
| Unicode Consortium | Unicoi, Tennessee | Unicon (programming language) |
| Unicornuate uterus | UNICOS | Unicycle |
| Unidentified flying object | UNIDO | Unification of Germany |
| Unified communications | Unified Extensible Firmware Interface | Unified Medical Language System |
| Unified Modeling Language | Unified Process | Unified shader model |
| Unified threat management | Uniform | Uniform distribution (continuous) |
| Uniform memory access | Uniform Resource Identifier | Uniform resource identifier |
| Uniform resource locator | Uniforms and insignia of the Schutzstaffel | Unikonta |
| Unilateral contact | Unilever | Unincorporated area |
| Uninflected word | Uninterruptible power supply | Union Bridge, Maryland |
| Union catalog | Union Center, Wisconsin | Union Charter Township, Michigan |
| Union City, Georgia | Union City, Indiana | Union City, Michigan |
| Union City, Tennessee | Union County, Indiana | Union County, Kentucky |
| Union County, New Jersey | Union County, Pennsylvania | Union County, South Carolina |
| Union des Sociétés Françaises de Sports Athlétiques | Union Films | Union Gap, Washington |
| Union Grove, Wisconsin | Union Hill, Illinois | Union List of Artist Names |
| Union of Christendom | Union of Islamic Organisations of France | Union of Soviet |
| Union of Soviet Socialist Republics | Union Parish, Louisiana | Union Point, Georgia |
| Union pour la démocratie française | Union pour un mouvement populaire | Union Springs, New York |
| Union Square, San Francisco | Union Township, Branch County, Michigan | Union Township, Grand Traverse County, Michigan |
| Union, Burnett County, Wisconsin | Union, Door County, Wisconsin | Union, Eau Claire County, Wisconsin |
| Union, Illinois | Union, Iowa | Union, Kentucky |
| Union, Mississippi | Union, Missouri | Union, Monroe County, West Virginia |
| Union, Nebraska | Union, Ohio | Union, Oregon |
| Union, Pierce County, Wisconsin | Union, Rock County, Wisconsin | Union, South Carolina |
| Union, Vernon County, Wisconsin | Union, Waupaca County, Wisconsin | UnionFS |
| Uniontown, Kansas | Uniontown, Kentucky | Uniontown, Washington |
| Unionville Center, Ohio | Unionville, Iowa | Unionville, Michigan |
| Uniopolis, Ohio | UniProt | Uniprot web |
| Unique Ingredient Identifier | Uniramia | UNIS |
| Unit (ring theory) | Unit 731 | Unit circle |
| Unit disk | Unit doses | Unit fraction |
| Unit of analysis | Unit of observation | Unit operation |
