An expression of regret in the general assembly (4)
I believe the answer is:
alas
'an expression of regret' is the definition.
(I've seen this before)
'in the general assembly' is the wordplay.
'in' says the answer is hidden in the clue.
'ALAS' is hidden in the letters of 'general assembly'.
(Other definitions for alas that I've seen before include "Expression of regret" , "express regret thus" , "Sad to say!" , "Regrettably, unfortunately" , "Sadly, unfortunately" .)