Fluid part of blood (6)
I believe the answer is:
plasma
'fluid part of blood' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for plasma that I've seen before include "Liquid part of blood" , "Colourless fluid in blood; green variety of quartz" , "Yellow liquid in blood" , "element of transfusion" , "Screens of some TVs" .)