Dilute (4)
I believe the answer is:
thin
'dilute' is the definition.
(I know that dilute can be written as thin)
This is all the clue.
(Other definitions for thin that I've seen before include "Sparse; not dense" , "as 7 [LOAF] may be sliced" , "Dilute; lean" , "Superficial" , "Lean; make (plants) less crowded" .)