Arterial way of vital importance (5)
I believe the answer is:
aorta
'vital importance' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'arterial way of' is the wordplay.
I cannot quite understand how this works, but
'way' could be 'r' (abbreviation for right) and 'r' is found within the answer.
'of' could be 'o' and 'o' is present in the answer.
The remaining letters 'ata' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "Large artery of the heart" , "Main artery from heart" , "Main human artery" , "One leads from heart" , "Main route from the heart" .)