Sad exclamation (4)
I believe the answer is:
alas
'sad exclamation' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alas that I've seen before include "Cry of woe" , "I'm sorry to say" , "Archaic exclamation of sorrow or regret" , "Regretfully!" , "Lackaday" .)