Mire (3)
'mire' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for fen that I've seen before include "Marshland" , "Water-logged area of vegetation" , "Low-lying wet land with grassy vegetation" , "Marshy area of land" , "One hundredth of a yuan" .)
'mire' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for mud that I've seen before include "soft soil" , "slander" , "Soft sticky earth" , "Mire" , "Sludge" .)
'mire' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sludge that I've seen before include "Ooze" , "Melting snow" , "Thick, soft, wet mud" , "Thick greasy mud" , "Muddy sediment" .)