Part of the respiratory system (7)
I believe the answer is:
trachea
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">part of the respiratory system</span>' is the definition.<br/ ><span class="explanation-format__explanation">('trachea' is part of 'respiratory system')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for trachea that I've seen before include "air passage" , "airway" , "Breathing tube" , "Tube taking inhaled air from the larynx" , "get air supply through this" .)