Theatrical lament (4)
I believe the answer is:
'theatrical lament' 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 "Oh dear!" , "Interjection of sorrow" , "By bad luck" , "What a shame!" , "Archaic exclamation of sorrow or regret" .)