Horror film includes a good trap? (8)
I believe the answer is:
carriage
'trap?' is the definition.
(thesaurus)
'horror film includes a good' is the wordplay.
'horror film' becomes 'carrie'.
'includes' is an insertion indicator.
'a good' becomes 'ag' (I've seen this in other clues).
'carrie' enclosing 'ag' is 'CARRIAGE'.
(Other definitions for carriage that I've seen before include "Comportment" , "Railway vehicle" , "Railway passenger coach" , "Conveyance (of items of merchandise)" , "Perhaps a smoker's" .)