Hound plague (3)
I believe the answer is:
dog
This clue is a double definition.
'hound' is the first definition.
(synonyms)
'plague' is the second definition.
(both can mean to follow or repeatedly torment)
(Other definitions for dog that I've seen before include "Sort of collar, fight, days" , "Follow; pet" , "boxer?" , "Cur" , "Follow closely; animal" .)