Dad’s high point, becoming vicar (6)
I believe the answer is:
pastor
'vicar' is the definition.
(thesaurus)
'dad's high point' is the wordplay.
'dad's' becomes 'pa's' ('pa' can be a synonym of 'dad').
'high point' becomes 'tor'.
'pas'+'tor'='PASTOR'
'becoming' is the link.
(Other definitions for pastor that I've seen before include "To spar with clergyman" , "Member of the clergy" , "Minister of religion" , "Church minister" , "Old shepherd" .)