Relating to blood vessels (8)
I believe the answer is:
vascular
'relating to blood vessels' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for vascular that I've seen before include "Relating to blood vessels" , "Of vessels that circulate blood" , "Relating to vessels that circulate fluids" , "Consisting of vessels for conveying blood" , "Relating to blood-carrying vessels" .)