All the fluid causing death (6)
I believe the answer is:
lethal
'causing death' is the definition.
(I've seen this before)
'all the fluid' is the wordplay.
'fluid' indicates anagramming the letters.
'all'+'the'='allthe'
'allthe' is an anagram of 'LETHAL'.
(Other definitions for lethal that I've seen before include "Enough to cause death" , "All the change can be deadly." , "very nasty indeed" , "bringing about the end?" , "bringing down the curtain" .)