The windpipe (7)
I believe the answer is:
trachea
'the windpipe' is the definition.
('trachea' can be a synonym of 'windpipe')
This is all the clue.
(Other definitions for trachea that I've seen before include "where air passes" , "membranous tube" , "It connects the larynx and bronchi" , "Breathing tube" , "Tube taking inhaled air from the larynx" .)