When the word coincidence was first attested in a 1626 natural history book by Francis Bacon, it referred to the condition of two things occupying the same space. A few decades later, it took on the additional meaning of "happening at the same time", and by the 1680s the "remarkable concurrence" definition also emerged. The word comes from the Latin verb coincidere, which is composed out of the prefix cum-, meaning "with", the prefix in-, meaning "into", and the verb cadere, meaning "to fall". As a whole, then, a coincidence was an event when things fell into each other. Cadere, which is also the root of words like cascade, decadaence, cadaver, and decay, comes (through Proto-Italic kado) from the Proto-Indo-European reconstruction khd, also meaning "to fall".
Hello! I'm Adam Aleksic, a rising junior studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy trivia, politics, vexillology, geography, board games, conlanging, art history, and law.