Horribly mean church to terrify (6)
I believe the answer is:
menace
'to terrify' is the definition.
(I've seen this in another clue)
'horribly mean church' is the wordplay.
'horribly' indicates anagramming the letters (a horribly wrong version of the letters).
'church' becomes 'CE' (abbreviation for Church of England).
'mean' anagrammed gives 'mena'.
'mena'+'ce'='MENACE'
(Other definitions for menace that I've seen before include "Harmful person" , "Intimidate" , "Threat, show of hostility" , "serious nuisance" , "Threaten with harm or danger" .)