ŝarko

A borrowing from English, which is rarer in this language than you would think. Esperanto's roots are overwhelmingly Romance with a Germanic and Slavic minority, and English contributes only a handful: ŝarko, boato, trajno, futbalo, budĝeto and not many more. When it does borrow from English it spells what it hears, so the sh becomes ŝ and the silent business at the end is tidied into -o. Written in the x-system for a keyboard that lacks the hats, it is sxarko.

The hat matters here. Ŝ is the sh of shop; plain s is the hiss of sit. So ŝarko is SHAR-ko and there is no such word as sarko. Compare sabro five ranks earlier, where the letter is a plain s and adding a hat would break it. Two words in one band, opposite errors, and the only defence is to type what you mean.

The company it keeps. Fiŝo is a fish at rank 1,031 and a shark technically is one; baleno at 2,440 is a whale and famously is not. Around them sit delfeno the dolphin, polpo the octopus and meduzo the jellyfish, and between them they are most of the sea that a beginner needs. The parts of this particular animal are worth a line: naĝilo is a fin - naĝi to swim plus the tool suffix -il-, so a fin is a swimming-tool, the same construction as tenilo ten ranks earlier in this band.

The figurative sense travelled with the word. As in English, a ŝarko can be a predatory human being: monŝarko for a loan shark, advokat-ŝarko for the kind of lawyer the phrase suggests. Given that one of the proposed etymologies has the fish named after the swindler rather than the reverse, that may be the older meaning coming home.