Exclamation of sorrow (5)
I believe the answer is:
alack
'exclamation of sorrow' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alack that I've seen before include "I'm sorry to say" , "Sadly" , "Previously expressed regret" , "I mourn" , "Old expression of dismay" .)