Serendipity

Unlike most English words that evolved gradually, "serendipity" has a precise birthday: January 28, 1754. The English writer Horace Walpole coined it in a letter, inspired by an old Persian fairy tale called The Three Princes of Serendip, in which the heroes "were always making discoveries, by accidents and sagacity, of things which they were not in quest of."

Serendip was an ancient name for Sri Lanka, derived from the Sanskrit Siṃhaladvīpa. For over a century after Walpole coined it, "serendipity" remained obscure — until twentieth-century scientists used it to describe accidental discoveries like Fleming's penicillin and Röntgen's X-rays. A 2004 survey named it the most difficult English word to translate.

Quarantine

"Quarantine" comes from the Italian quaranta giorni, meaning "forty days." During the Black Death in the 14th century, ships arriving in Venice were required to anchor offshore for forty days before passengers could disembark. The number forty had biblical significance, but the medical reasoning — that diseases would manifest within that window — was sound.

Robot

"Robot" is one of the few English words borrowed directly from Czech. It first appeared in Karel Čapek's 1920 play R.U.R. (Rossum's Universal Robots). Čapek's brother Josef suggested the word, derived from the Czech robota, meaning forced labor or drudgery. Within a few years it had entered every major European language.