Get out in the open (3)
I believe the answer is:
air
'get out in the open' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for air that I've seen before include "Ventilate or give expression to" , "Mixture of gases required for breathing" , "Song; ventilate" , "Ambience" , "Sky" .)