Swampy ground (4)
I believe the answer is:
mire
'swampy ground' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for mire that I've seen before include "Bog down in swamp" , "Stretch of boggy ground" , "(Stretch of) clinging mud" , "Soft mud or dirt" , "Morass" .)