Meddler (8)
'meddler' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for busybody that I've seen before include "Person who meddles in the affairs of others" , "Proactive meddler" , "One minds everyone else's business" , "he'll nose around" , "Meddling person" .)
(Other definitions for interloper that I've seen before include "one who gatecrashes" , "Uninvited attendee" , "Intruder" , "one entering uninvited" .)