Exclamation of woe (4)
I believe the answer is:
alas
'exclamation of woe' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alas that I've seen before include "Expression of regret" , "Regretfully!" , "Archaic exclamation of sorrow or regret" , "Too bad, so sad" , "Expression of grief/pity" .)