The Collaborative International Dictionary of English v.0.48:

Khan \Khan\, n. [Pers. & Tart. kh[=a]n.] [Also kan, kaun.]
   A king; a prince; a chief; a governor; -- so called among the
   Tartars, Turks, and Persians, and in countries now or
   formerly governed by them.
   [1913 Webster]