Monastery head (5)
(Other definitions for prior that I've seen before include "More pressing" , "Abbott's deputy being earlier?" , "Antecedent" , "former conviction" , "writer of epigrammatic verse" .)
'monastery head' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abbot that I've seen before include "first in order" , "Monks' leader" , "Head of group of monks" , "Head of religious house" , "Monastery chief" .)