Lost blood (4)
I believe the answer is:
bled
'lost blood' is the definition.
('bleed' can be a synonym of 'lose blood')
This is the entire clue.
(Other definitions for bled that I've seen before include "Haemorrhaged" , "Showed effects of injury" , "Lost blood" , "Extracted blood as treatment" , "Seeped (into an adjoining colour)" .)