The body's biggest artery (5)
I believe the answer is:
aorta
'the body's biggest artery' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aorta that I've seen before include "One leads from heart" , "Main human artery" , "Trunk route" , "it's drawing blood!" , "Main artery of body" .)