One old ruin greatly admired (4)
I believe the answer is:
idol
'one old ruin greatly admired' is the definition.
I can't tell whether this defines the answer.
'one old ruin' is the wordplay.
'one' becomes 'i' (Roman numeral).
'ruin' indicates anagramming the letters.
'old' anagrammed gives 'dol'.
'i'+'dol'='IDOL'
Can you help me to learn more?
(Other definitions for idol that I've seen before include "Superstar; graven image" , "'Worshipped object, admired person (4)'" , "One much admired" , "Object of reverence" , "A graven image or object of adoration" .)