Crucial artery (5)
I believe the answer is:
aorta
'crucial artery' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aorta that I've seen before include "vital transporter" , "Main arterial vessel, carrying blood to the heart" , "Main artery of body" , "Bloody channel" , "Main human artery" .)