When the word agenda was first borrowed into the English language in the seventeenth century, it was used in a theological context to refer to religious practices that were carried out, unlike its counterpart credenda, which was reserved for religious beliefs that were more theoretical. Both terms come from Latin, where agenda literally meant "things to be done" since it was a gerund of the verb agere, "to do". That, through Proto-Italic, is believed to derive from the Proto-Indo-European root ag, which had to do with movement. Agenda got where it is today because the definition evolved from "religious practices" to "a written set of religious rituals" to "items of business". By the twentieth century, it came to be associated with planners, and usage in literature over time peaked in 2003.
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.