karbo

Coal is not carbon, and Esperanto is strict about it. Karbo is the black stuff you burn: mineral coal, and by extension charcoal. The chemical element is karbono, a separate word, and the two are not interchangeable in any register. Karbona dioksido is carbon dioxide; karba minejo is a coal mine. Esperanto is doing here what it does throughout its scientific vocabulary - taking the international scientific term for the science and keeping the ordinary root for ordinary life - and this chapter's companion reading on scientific Esperanto sets out the principle. English blurs the two (a carbon footprint is really a coal-and-oil footprint), which is precisely why the distinction is worth learning in a language that does not.

The compounds do the sorting. Ŝtonkarbo is mineral coal, lignokarbo is charcoal made from ligno at 719, brunkarbo is lignite, and karbigi is to char something. Karbisto is the coalman and karbejo the coal cellar. Karba as an adjective covers anything to do with coal, so karba industrio is the coal industry.

A word carrying a century of history. Karbo sits at rank 2,798 in a corpus drawn from 1887 to 1930, which is to say from the period when coal was simply what powered everything: the trains, the ships that carried the delegates to the congresses, the forno at 1,577 in every kitchen. Reading Esperanto of that era, you meet it constantly and in a register of plain fact rather than of politics. That register has since changed completely, and the word has not.