18-letter words containing a, d, i, t, u, s
- 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.
- urban homesteading — homesteading (def 2).
- white man's burden — the alleged duty of white colonizers to care for nonwhite indigenous subjects in their colonial possessions.
- wildlife sanctuary — an area where wild animals and plants are protected
- yeast nucleic acid — RNA.