Almost the finest of ancient cities (6)
I believe the answer is:
thebes
'of ancient cities' is the definition.
The definition suggests a singular noun which matches the answer.
'almost the finest' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'finest' becomes 'best' (similar in meaning).
'the'+'best'='thebest'
'thebest' with its last letter removed is 'THEBES'.
Can you help me to learn more?
(Other definitions for thebes that I've seen before include "Classical city" , "Ancient Nile city" , "Ancient city of upper Egypt" , "Old city of Greece or Egypt" , "Old Egyptian city" .)