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