Trench in meadow ending with silt (4)
I believe the answer is:
leat
'trench' is the definition.
(a leat is a trench carrying water to a mill)
'meadow ending with silt' is the wordplay.
'meadow' becomes 'lea' (a lea is a grassy area).
'ending with' says to take the final letters.
The final letter of 'silt' is 't'.
'lea'+'t'='LEAT'
'in' acts as a link.
(Other definitions for leat that I've seen before include "Mill water channel" , "millstream" , "Mill stream" , "Water trench" .)