"Ah, well!" (4)
I believe the answer is:
alas
'ah well' 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 "Interjection of sorrow" , "Cry of woe" , "Sad to say!" , "Regrettably, unfortunately" , "Unhappily" .)