Prophet pens new insult (5)
I believe the answer is:
sneer
'insult' is the definition.
(thesaurus)
'prophet pens new' is the wordplay.
'prophet' becomes 'seer' (both can mean someone who tells the future).
'pens' is an insertion indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'seer' placed around 'n' is 'SNEER'.
(Other definitions for sneer that I've seen before include "Show cynical contempt" , "Smile contemptuously" , "Contemptuous expression" , "Show contempt with scornful expression or words" , "Express cynical contempt" .)