rublo

The rouble, unit of Russian money, spelled the British way in the translation and pronounced the Esperanto way: ROO-blo, both syllables clean, no schwa. It joins franko and dolaro and pundo on the short list of currencies that got their own root rather than a description.

That this word is here at all is a small piece of history. Esperanto was published in Warsaw in 1887, in the Russian Empire, by a man whose first readers paid in roubles; the early movement's accounts, subscriptions and prizes are all denominated in them. A frequency list built on real Esperanto text picks that up. The same current puts bojaro, a Russian noble, at rank 807.

A near-pair worth naming. Rubo, at rank 2056 in this same stretch of the list, means rubbish or rubble. Rublo is money and rubo is what you throw out, and they differ by one letter. Nothing links them: rubo comes from the international rubbish family and rublo from the Russian for chopping silver. Esperanto is unusually forgiving of typing errors because words are long and endings are grammatical, but this is a pair where the l carries the whole meaning.