.... Enrico; about to ruin ours (6)
I believe the answer is:
'enrico' is the definition.
Both the definition and answer are singular nouns.
Maybe you can see a link between them that I don't see?
'about to ruin ours' is the wordplay.
'about' becomes 'ca' (short for circa).
'to ruin' indicates anagramming the letters.
'ours' is an anagram of 'ruso'.
Can you help me to learn more?
(Other definitions for caruso that I've seen before include "Opera singer", "Enrico ...... was famous Italian tenor", "Enrico -, twentieth century Italian tenor", "Classical tenor", "Singer Enrico".)