Breathe it in! (3)
I believe the answer is:
air
'breathe it in' 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 "Refrain" , "Ventilate with oxygen" , "Ventilate, give voice to" , "strain" , "Mixture of gases required for breathing" .)