WordNet (r) 3.0 (2006):

UK
    n 1: a monarchy in northwestern Europe occupying most of the
         British Isles; divided into England and Scotland and Wales
         and Northern Ireland; `Great Britain' is often used loosely
         to refer to the United Kingdom [syn: United Kingdom,
         UK, U.K., Britain, United Kingdom of Great Britain
         and Northern Ireland, Great Britain]

The Free On-line Dictionary of Computing (30 December 2018):

uk

    The country code for United Kingdom.

   (1999-01-27)