The Collaborative International Dictionary of English v.0.48:

Taxiarch \Tax"i*arch\, n. [Gr. ? and ?; ? a division of an army,
   a brigade (from ? to arrange, array) + to rule.] (Gr. Antiq.)
   An Athenian military officer commanding a certain division of
   an army. --Milford.
   [1913 Webster]