Wet soil (3)
'wet soil' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mud that I've seen before include "-, -, Glorious - (Flanders and Swann)" , "In your eye, this is an informal toast" , "Soft sticky earth" , "Clay" , "Adverse comments" .)
(Other definitions for mire that I've seen before include "(Stretch of) clinging mud" , "Marsh" , "Emir found in mud" , "Bog down in swamp" , "Morass" .)