Unusually prosaic about ordinary large rock in Athens (9)
I believe the answer is:
acropolis
'rock in athens' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'unusually prosaic about ordinary large' is the wordplay.
'unusually' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'ordinary' becomes 'O' (abbreviation eg in O-Level, Ordinary Level).
'large' becomes 'L' (eg in clothes sizes).
'prosaic' with letters rearranged gives 'acropis'.
'o'+'l'='ol'
'acropis' going around 'ol' is 'ACROPOLIS'.
Can you help me to learn more?
(Other definitions for acropolis that I've seen before include "classical site" , "high point" , "Imposing building" , "Parthenon location" , "old citadel" .)