One inquisitive policeman by corpse (8)
I believe the answer is:
busybody
'one inquisitive' is the definition.
(someone who is inquisitive)
'policeman by corpse' is the wordplay.
'policeman' becomes 'busy' (informal UK term for a police officer).
'by' means one lot of letters go next to another.
'corpse' becomes 'body' (I've seen this before).
'busy'+'body'='BUSYBODY'
(Other definitions for busybody that I've seen before include "A meddlesome person, certainly not idle" , "butter in" , "Prying person" , "he'll nose around" , "Person who meddles in the affairs of others" .)