Uttered expression of regret over dead so-called city once (6)
I believe the answer is:
saigon
'uttered expression' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'regret over dead so-called city once' is the wordplay.
I cannot really see how this works, but
'over' could be 'on' (physically on top of) and 'on' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for saigon that I've seen before include "city in Asia" , "See 8" , "Asian city once" , "Musical set in Vietnam war - ''Miss . . . . . .''" , "Former South Vietnamese capital" .)