When the word ditto was borrowed into English in 1625, it was only used to replace the month name in accounts of dates, to avoid hand cramping due to copying the same term over and over again. 53 years later, people figured out that they can use ditto in any context where a list contains repetition, and the rest is history. In the original Tuscan, ditto meant "the said" (as in, something that was already said), which is a variation of Italian detto. Detto in turn is from the Latin verb dire, or "to say", which is a contraction of the infinitive dicere, "to speak". Finally, through Proto-Italic, dicere derives from the Proto-Indo-European reconstruction deik, meaning "to show". Ditto was especially popular in the 1770s and has been decreasing in usage since then, despite a small resurgence in the 1940s.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.