Fine sand (4)
I believe the answer is:
silt
'fine sand' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for silt that I've seen before include "Sediment deposited by a river" , "Mud deposited in a river or lake" , "Fine deposited material" , "Jamboree" , "Slimy mud" .)