Preoccupies (6)
I believe the answer is:
haunts
'preoccupies' is the definition.
(haunting is a kind of preoccupying)
This is the entire clue.
(Other definitions for haunts that I've seen before include "Frequently visits" , "Inhabits as a ghost" , "Frequently visited places, hangouts" , "Visits like a ghost" , "Frequents or visits as a ghost" .)