The Collaborative International Dictionary of English v.0.48:

Yataghan \Yat"a*ghan\, n. [Turk. y[=a]t[=a]gh[=a]n.]
   A long knife, or short saber, common among Mohammedan
   nations, usually having a double curve, sometimes nearly
   straight. [Written also ataghan, attaghan.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Attaghan \At"ta*ghan\ ([a^]t"t[.a]*g[a^]n), n.
   See Yataghan.
   [1913 Webster]