• U-boat
• U-bolt
• U-bolt clamp
• U-clamp terminal
• U-tube exchanger
• U-turn
• U.S. District Court Am.
• U/W : underwriter
• UEFA : Union of European Football Associations
• UFO : unidentified flying object
• UHF : ultrahigh frequency
• UHT milk
• UIE : UNESCO Institute for Education
• UK : United Kingdom
• UN
• UNCC : United Nations Compensation Commission
• UNCCD : Secretariat of the United Nations Convention to Combat Desertification
• UNCDF : United Nations Capital Development Fund
• UNCHS : United Nations Centre for Human Settlements
• UNCITRAL : United Nations Commission on International Trade Law
• UNCRD : United Nations Centre for Regional Development
• UNCTAD : United Nations Conference on Trade and Development
• UNDCP : United Nations International Drug Control Programme
• UNDP : United Nations Development Programme
• UNEP : United Nations Environment Programme
• UNESCO : United Nations Educational, Scientific, and Cultural Organization
• UNEVOC : International Centre for Technical and Vocational Education and Training
• UNFCCC : Secretariat of the United Nations Framework Convention on Climate Change
• UNFPA : United Nations Population Fund
• UNHCHR : United Nations High Commissioner for Human Rights
• UNHCR : United Nations High Commissioner for Refugees
• UNICEF : United Nations Children's Fund
• UNICRI : United Nations Interregional Crime and Justice Research Institute
• UNIDIR : United Nations Institute for Disarmament Research
• UNIDO : United Nations Industrial Development Organizatio
• UNIFEM : United Nations Development Fund for Women
• UNMOVIC : United Nations Monitoring, Verification and Inspection Commission
• UNO : United Nations
• UNOPS : United Nations Office for Project Services
• UNOV : United Nations Office at Vienn
• UNRISD : United Nations Research Institute for Social Development
• UNRWA : United Nations Relief and Works Agency for Palestinian Refugees in the Near East
• UNSCEAR : United Nations Scientific Committee on the Effects of Atomic Radiation
• UNU : United Nations University
• UNV : United Nations Volunteers
• UOK : Are you okay?
• UPI : United Press International
• UPS : United Parcel Service
• UPS : uninterruptable power supply
• UPU : Universal Postal Union
• US : United States
• USA : United States of America
• USAF : United States Air Force
• USB : universal serial bus
• USB keychain
• USDA : United States Department of Agriculture
• USSR : Union of Socialist Soviet Republics
• USW : ultrashort wave
• UTB : urgent toilet break
• UV : ultraviolet
• UV light
• UV resistance
• Udmurtia
• Ufa
• Uganda
• Uganda Woodland Warbler
• Ugandan
• Ugh! Disgusting!
• Ujungpandang
• Ukraine
• Ukrainian
• Ulaanbaatar
• Ulsan
• Ulster Defence Association
• Ultramarine Grosbeak
• Ultramarine Kingfisher
• Ultramarine Lory
• Uluguru Violet-backed Sunbird
• Unadorned Flycatcher
• Uncle Sam Am.
• Undulated Antpitta
• Undulated Antshrike
• Undulated Tinamou
• Unfortunately !
• Unfortunately, we can't produce the money for it just like that.
• Unhappy Monarch
• Unicoloured Antwren
• Unicoloured Blackbird
• Unicoloured Jay
• Unicoloured Tapaculo
• Unicoloured Thrush
• Uniform Antshrike
• Uniform Crake
• Uniform Finch
• Uniform Swiftlet
• Uniform Treehunter
• Union Jack
• United Arab Emirates
• United Kingdom of Great Britain and Northern Ireland
• United Socialist Party