Positive place, America (4)
I believe the answer is:
plus
'positive' is the definition.
('plus' can be similar in meaning to 'positive')
'place america' is the wordplay.
'place' becomes 'pl' (I've seen this in other clues).
'america' becomes 'us' (abbreviation for the United States).
'pl'+'us'='PLUS'
(Other definitions for plus that I've seen before include "Together with; advantage" , "Positive sign" , "To the French it's more" , "Coupled with" , "mark for arithmetic" .)