vulkano

A god's name that became a common noun. Vulcan was the Roman blacksmith god, and the Romans decided his forge was under the island of Vulcano in the Aeolian chain, because it smoked. When Europeans went looking for a word for smoking mountains in general, they used the island's name, and every language in Esperanto's source list had already done it: volcan, vulcano, Vulkan, volcano. Zamenhof did not have a decision to make.

A false seam worth naming. Vulkano looks like it could be vulk- plus -an-, the member suffix that gives kristano a Christian and urbano a townsperson. It is not: there is no root vulk-, and a volcano is not a member of anything. One root, borrowed whole. The same trap catches oceano and vegetarano, one of which really does end in the suffix.

And the other half of the pair. Raketo sits two ranks further on at 2,836, which gives this band a launch and an eruption side by side. They are the same physics, roughly: hot gas leaving fast in one direction and pushing everything else in the other. A volcano is just an unusually badly aimed rocket.

Vocabulary the root gives away. Vulkana is volcanic, vulkanisto is a volcanologist, vulkanizi is to vulcanise rubber, which Charles Goodyear named after the same god because the process needs heat. Cindro at 2,260 is the ash and lafo is the lava.