Advantage; positive (4)
I believe the answer is:
plus
I believe this is a double definition.
'advantage' is the first definition.
(a plus is an advantage or benefit)
'positive' is the second definition.
(I know that positive can be written as plus)
(Other definitions for plus that I've seen before include "An advantage (colloq.)" , "Something more" , "Benefit" , "being a little cross" , "asset" .)