Wet spongy earth
I believe the answer is:
mire
'wet spongy earth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mire that I've seen before include "Soft mud or dirt" , "(Stretch of) clinging mud" , "Deep soft mud" , "Stretch of boggy ground" , "Bog down in swamp" .)