Oppressive old emperor no longer working (7)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

O (old) + NERO (emperor) + U/S (unserviceable, no longer working). I cannot wait to see Simon apologise on behalf of all setters everywhere for this barely explicable abbreviation. “It’s not just any word, you know”, it’s pretty much any word, and any number of letters, with random punctuation in between that’s completely ignored.