Large artery (5)
I believe the answer is:
aorta
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large artery</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for aorta that I've seen before include "Tube" , "vital transporter" , "Major artery of the body" , "Principal artery" , "Large blood-vessel" .)