Lament, grieve (5)
I believe the answer is:
mourn
I believe this is a double definition.
'lament' is the first definition.
(I've seen this in another clue)
'grieve' is the second definition.
(I know that mourn is a kind of grieve)
(Other definitions for mourn that I've seen before include "Keen" , "Show sorrow for loss" , "Show sorrow at death" , "Be sad over loss" , "Grieve for a death" .)