The Collaborative International Dictionary of English v.0.48:

Kuklux \Ku`klux"\, Ku Klux \Ku` Klux"\, Ku Klux Klan \Ku` Klux"
Klan\, n.
   The name adopted in the southern part of the United States by
   a secret political organization, active for several years
   after the close of the Civil War, and having for its aim the
   repression of the political power of the freed negroes; --
   called also Kuklux Klan and the Klan. It exerienced a
   revival in the 1920's, in the north as well as the south, and
   persists as a weak organization into the 1990's. Its goals
   were primarily anti-negro and anti-Catholic, and its tactics
   included terrorist attacks on negroes for the purpose of
   intimidation with the goal of continuing segregation. The
   signature activity of the Klan was the burning of a cross,
   either at rallies of Klansmen, or on the property of
   African-Americans which they hoped to intimidate.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Ku Klux Klan
    n 1: a secret society of white Southerners in the United States;
         was formed in the 19th century to resist the emancipation
         of slaves; used terrorist tactics to suppress Black people
         [syn: Ku Klux Klan, Klan, KKK]