Respiratory tube (7)
I believe the answer is:
trachea
'respiratory tube' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for trachea that I've seen before include "get air supply through this" , "The formal windpipe" , "pipe" , "Tube carrying air to the lungs" , "Tube taking inhaled air from the larynx" .)