Be nosy (3)
I believe the answer is:
pry
'be nosy' is the definition.
(to pry is to investigate nosily)
This is all the clue.
(Other definitions for pry that I've seen before include "Interfere" , "Be inquisitive" , "Stick one's nose in" , "Intrusively enquire" , "Stick nose into other's business" .)