Definition of hierarch in English:
 hierarch
noun ˈhʌɪərɑːkˈhaɪ(ə)ˌrɑrk
- A chief priest, archbishop, or other leader. -  Example sentencesExamples -  Certainly there have been notable Orthodox hierarchs in this country and abroad, many of them Russians, whose vision of Orthodoxy and its catholic mission was a resplendent one.
-  A postulant who wishes to enter the spiritual life has a sponsor who presents him to the hierarch.
-  There is a mosaic in Ravenna portraying saints, martyrs, hierarchs, and faithful laity, each of them holding a crown that they will place at the feet of Christ.
-  The works of their most respected theologians and thinkers are not only still unavailable in most of Russia's seminaries, but are also viewed by many hierarchs as heretical.
-  Thirteen bishops of Great Russian origin and merely two Ukrainian hierarchs were consecrated in the 1760s.
-  Anselm of Canterbury, eleventh-century theologian, monk and Church hierarch, is arguably the major figure in the theological road from Augustine to Aquinas.
 
Origin
  
Late Middle English: via medieval Latin from Greek hierarkhēs, from hieros 'sacred' + arkhēs 'ruler'.
Definition of hierarch in US English:
 hierarch
nounˈhī(ə)ˌrärkˈhaɪ(ə)ˌrɑrk
- A chief priest, archbishop, or other leader. -  Example sentencesExamples -  A postulant who wishes to enter the spiritual life has a sponsor who presents him to the hierarch.
-  Anselm of Canterbury, eleventh-century theologian, monk and Church hierarch, is arguably the major figure in the theological road from Augustine to Aquinas.
-  Thirteen bishops of Great Russian origin and merely two Ukrainian hierarchs were consecrated in the 1760s.
-  The works of their most respected theologians and thinkers are not only still unavailable in most of Russia's seminaries, but are also viewed by many hierarchs as heretical.
-  There is a mosaic in Ravenna portraying saints, martyrs, hierarchs, and faithful laity, each of them holding a crown that they will place at the feet of Christ.
-  Certainly there have been notable Orthodox hierarchs in this country and abroad, many of them Russians, whose vision of Orthodoxy and its catholic mission was a resplendent one.
 
Origin
  
Late Middle English: via medieval Latin from Greek hierarkhēs, from hieros ‘sacred’ + arkhēs ‘ruler’.