The Collaborative International Dictionary of English v.0.48:

Seppuku \Sep*pu"ku\, n.
   Same as Hara-kiri.
   [1913 Webster]

         Seppuku, or hara-kiri, also came into vogue. --W. E.
                                                  Griffis.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seppuku
    n 1: ritual suicide by self-disembowelment on a sword; practiced
         by samurai in the traditional Japanese society [syn:
         harakiri, hara-kiri, harikari, seppuku]