Herbert upset by new monks (8)
I believe the answer is:
brethren
'monks' is the definition.
(I've seen this before)
'herbert upset by new' is the wordplay.
'upset by' is an anagram indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'herbert' with letters rearranged gives 'brethre'.
'brethre'+'n'='BRETHREN'
(Other definitions for brethren that I've seen before include "Brothers; Plymouth -" , "Ancient brothers" , "Colleagues (in sect)" , "Kindred" , "Church members" .)