Attenuated (4)
I believe the answer is:
thin
'attenuated' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thin that I've seen before include "Sparse; not dense" , "Scrawny" , "Lean; make (plants) less crowded" , "With little thickness" , "Slender, slight" .)