Irritate rector with terrible lie (4)
I believe the answer is:
rile
'irritate' is the definition.
(I know that irritate can be written as rile)
'rector with terrible lie' is the wordplay.
'rector' becomes 'r' ().
'with' means one lot of letters go next to another.
'terrible' is an anagram indicator.
'lie' is an anagram of 'ile'.
'r'+'ile'='RILE'
(Other definitions for rile that I've seen before include "Provoke" , "Lire (anag)" , "Irk" , "Exasperate" , "Anger, annoy" .)