It's in the air (6)
I believe the answer is:
oxygen
'it's in the air' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oxygen that I've seen before include "Gas required for life" , "publicity, perhaps" , "Abundant gas" , "Element essential for animal life" , "Most abundant element in the earth's crust" .)