Grief or deep sadness (6)
I believe the answer is:
sorrow
This clue is a double definition.
'grief' is the first definition.
(I know that grief can be written as sorrow)
'deep sadness' is the second definition.
(I've seen this before)
(Other definitions for sorrow that I've seen before include "Woe" , "'Distress, sadness (6)'" , "Deep distress" , "Shakespeare: ''Parting is such sweet . . . . . .'' (6)" , "Unhappiness" .)