Meddlesome person occupied with main part (8)
I believe the answer is:
busybody
'meddlesome person' is the definition.
(I've seen this before)
'occupied with main part' is the wordplay.
'occupied' becomes 'busy' ('busy' can be similar in meaning to 'occupied').
'with' says to put letters next to each other.
'main part' becomes 'body' (I've seen this before).
'busy'+'body'='BUSYBODY'
(Other definitions for busybody that I've seen before include "Nosey Parker" , "One minds everyone else's business" , "Proactive meddler" , "Meddling person" , "A meddlesome interfering person" .)