The Collaborative International Dictionary of English v.0.48:

Haiduck \Hai"duck\ (h[imac]"d[.u]k), n. [G. haiduck, heiduck,
   fr. Hung. hajdu.]
   Formerly, a mercenary foot soldier in Hungary, now, a
   halberdier of a Hungarian noble, or an attendant in German or
   Hungarian courts. [Written also hayduck, haiduk,
   heiduc, heyduck, and heyduk.]
   [1913 Webster]