The Collaborative International Dictionary of English v.0.48:

Hierarch \Hi"er*arch\ (h[imac]"[~e]r*[aum]rk`), n. [LL.
   hierarcha, Gr. ?; "iero`s sacred (akin to Skr. ishiras
   vigorous, fresh, blooming) + ? leader, ruler, fr. ? to lead,
   rule: cf. F. hi['e]rarque.]
   One who has high and controlling authority in sacred things;
   the chief of a sacred order; as, princely hierarchs.
   --Milton. Hierarchal

WordNet (r) 3.0 (2006):

hierarch
    n 1: a person who holds a high position in a hierarchy
    2: a senior clergyman and dignitary [syn: archpriest,
       hierarch, high priest, prelate, primate]