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Douglas Harper's Etymology Dictionary
U.K.

abbreviation of United Kingdom, attested from 1883.

Wikipedia
U.K. (band)

U.K. are a British progressive rock supergroup originally active from 1977 until 1980. The band was composed of singer/bassist John Wetton (formerly of King Crimson, Roxy Music, Bryan Ferry's band and Uriah Heep), keyboardist/electric violinist Eddie Jobson (formerly of Curved Air, Roxy Music and Frank Zappa's band), guitarist Allan Holdsworth (formerly of Tempest, Soft Machine, The New Tony Williams Lifetime and Gong) and drummer Bill Bruford (formerly a full member of Yes and King Crimson, and also a tour drummer for Genesis), later replaced by drummer Terry Bozzio (formerly of Frank Zappa's band). UK reformed with John Wetton, Eddie Jobson and Terry Bozzio for a world tour in 2012.

U.K. (album)

U.K. is the self-titled debut album by the progressive rock supergroup U.K., released in May 1978 through E.G. Records and Polydor Records. It features John Wetton, Eddie Jobson, Bill Bruford, and Allan Holdsworth. "In the Dead of Night" and "Mental Medication" were both edited for single release. The album was well received by FM album rock radio and by the public during the summer of 1978. The LP sold just over 250,000 copies by 1 September 1978, with further sales thru the balance of the year.

In 2015 Rolling Stone magazine ranked it as the 30th best progressive rock album of all time.