Poisonous fluid (5)
I believe the answer is:
venom
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">poisonous fluid</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for venom that I've seen before include "Snake's poison" , "acrimony" , "Poisonous fluid" , "Bitter malice" , "Virulent feeling" .)