Ooze, muck (5)
I believe the answer is:
slime
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">ooze</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that ooze can be written as slime)</span><br/ ><br/ >'<span class="explanation-format__original">muck</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that muck can be written as slime)</span><br/ ><br/ ></span>
(Other definitions for slime that I've seen before include "Slippery mud; slug trail" , "Gunge" , "Gunk" , "Moist slippery stuff" , "Sludge, gloop" .)