Pain in the neck, pest (8)
I believe the answer is:
nuisance
This clue is a double definition.
'pain in the neck' is the first definition.
(synonyms)
'pest' is the second definition.
(both can mean an annoying person)
(Other definitions for nuisance that I've seen before include "Tiresome person or event" , "Pest or irritation" , "Bothersome pest" , "troublesome type" , "Annoying person/thing" .)