18-letter words containing u, d, a, i
- united arab states — a former (1958–61) federation of the United Arab Republic (Egypt and Syria) and Yemen.
- united nations day — the anniversary of the United Nations on October 24, marking its founding in 1945.
- united states army — the permanent or regular military land force of the United States, under the authority of the Department of Defense since 1947. Abbreviation: USA.
- united states navy — the permanent or regular naval force of the United States, under the authority of the Department of Defense since 1947. Abbreviation: USN.
- universal debugger — (tool, parallel) (udb) KSR's interactive source level debugger for serial and parallel programs written in KSR, Fortran, KSR C and KSR1 assembly language. Udb is a source level debugger for testing and debugging serial and parallel programs; it is compatible with GDB and dbx. The user can direct udb either by typing commands or graphically through an X-based window interface; the latter provides simultaneous display of source code, I/O and instructions. For parallel programs, operations can be carried out per-thread.
- upper middle class — wealthy, highly-educated people
- urban homesteading — homesteading (def 2).
- vanadium pentoxide — a yellow to red crystalline compound, V 2 O 5 , slightly soluble in water, used as a catalyst for organic reactions, in glass to absorb ultraviolet radiation, and as a photographic developer.
- video surveillance — a system of monitoring activity in an area or building using a television system in which signals are transmitted from a television camera to the receivers by cables or telephone links forming a closed circuit
- white man's burden — the alleged duty of white colonizers to care for nonwhite indigenous subjects in their colonial possessions.
- widemouth blindcat — any of several catfishes, as Satan eurystomus (widemouth blindcat) of Texas, that inhabit underground streams and have undeveloped eyes and unpigmented skin.
- wildlife sanctuary — an area where wild animals and plants are protected
- wrongful dismissal — the act of making someone redundant for reasons which are illegal or unjust
- xenon hexafluoride — a colorless, crystalline compound, XeF 6 , that melts at 50°C to a yellow liquid, and boils at 75°C.
- yeast nucleic acid — RNA.