Definition of xi in English:



  • 1The fourteenth letter of the Greek alphabet (Ξ, ξ), transliterated as ‘x.’

    • ‘While having no Latin derivative, the Xi was adopted into the early Cyrillic alphabet, as the letter ksi.’
    • ‘This page displays the Greek alphabet and gives information on pronunciation for both ... y as in yet, and before gamma, kappa, xi, or chi.’
    1. 1.1Astronomy [followed by Latin genitive]The fourteenth star in a specified constellation.
      ‘Xi Cygni’
      • ‘The highlight for me that night was Xi Bootes. This colorful double lies about 8 degrees east of Arcturus.’