Slimy secretion (5)
I believe the answer is:
mucus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">slimy secretion</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 mucus that I've seen before include "Slimy secretion of nose" , "Phlegm" , "Snot" , "Thick, slimy stuff" , "Nasal secretion" .)