Lifeblood (7)
I believe the answer is:
essence
'lifeblood' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for essence that I've seen before include "Vital part of something" , "Cologne, perhaps?" , "Concentration; nub" , "Concentrated liquid flavouring" , "Core, most vital part" .)