In 1887, a Polish ophthalmologist named Ludwik Lejzer Zamenhof published the most influential book in conlanging history - Unua Libro (or "First Book"), which laid the foundation for Esperanto. He wanted this to be a universal auxiliary language, which never quite happened, but to this day there are several thousand native speakers and a very dedicated base. It was still a good hope, however, which was probably why Zamenhof signed the book with a pseudonym meaning "one who hopes", or Esperanto. Since he never named his language, early adopters latched onto his pen name, and that's why we call it Esperanto today. That word wasn't pulled from thin air, however: Zamenhof created it from the Latin verb sperare, meaning "to hope", which is coincidentally the etymon of both the English words despair and prosper (coming from Proto-Indo-European speh, meaning "to turn out well").
Adam Aleksic, an incoming freshman at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd