Sad -- unlike this clue? (4)
I believe the answer is:
down
'sad' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for down that I've seen before include "Feathers or hair" , "Out of sorts" , "like the other set of clues" , "Depressed - drink" , "Pillow filler - dejected" .)