Source : Webster's Revised Unabridged Dictionary (1913)

Fin de siecle \Fin` de si[`e]"cle\ [F.]
   Lit., end of the century; -- mostly used adjectively in
   English to signify: belonging to, or characteristic of, the
   close of the 19th century; modern; ``up-to-date;'' as,
   fin-de-si[`e]cle ideas.

Source : WordNet®

fin de siecle
     adj : relating to or characteristic of the end of a century
           (especially the end of the 19th century); "fin de
           siecle art"