Back part of flat road used to deliver blood (5)
I believe the answer is:
aorta
'blood' is the definition.
The definition and answer can be both body parts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'back part of flat road used' is the wordplay.
'back' shows that the letters should be reversed in order.
'part of' indicates a hidden word.
'atroa' is hidden within 'flat road used'.
'atroa' written backwards gives 'AORTA'.
'to deliver' is the link.
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "vital transporter" , "A rota (anag)" , "Main route from the heart" , "Major artery of the body" , "Main artery from heart" .)