[thaumasiotes]

The Greek word meant "alone". Thus an oligarch rules in company with a small group of other people, but a monarch rules alone.

Internal to Greek, mon- was the conventional prefix for a meaning of "one", despite the word for "one" being different. This didn't happen in Latin, where the numeric prefix uni- ["one"] derives from unus ["one"] and not from solus ["alone"].

The Chinese terms have preserved a robust distinction between "one", the number, and "alone", the state of being. It's a strange choice, though, to offer different translations for the same concept in two closely related words. That distinction isn't in place in the original words.

[eszed]

I was aware of the Greek - but (sadly) didn't study Latin, so thanks.

I may not have understood your point, though. Do you object to this particular translation (which seems fine to me? Basically, "[thing] is singular [in this set]"), or just that English is a cursed bastard of a language - which, you know, means dragging in the Latin-derived "singular" along with the Greek mon- words might have been the simplest, albeit even more impure, route to clarity. (I'm reminded of AE Houseman's sniffy distaste for the word "homosexual": "half-Latin, half-Greek? That'll never do.")