When the word protest was first used in English around 1560, it meant "formal declaration" (this is the same sense as in the noun Protestant, which described people who formally declared independence from the Catholic Church). Through Old French protester, it traces to Latin protestari, also meaning "publicly declare" but having a more literal translation of "testify before". That's because it's composed of the prefix pro-, meaning "before" or "in front of" in this context (from Proto-Indo-European per, "forward"), and the root testis, meaning "witness" (also the etymon of testify, testament, and testicle; from the Proto-Indo-European word for "three", tris). The idea was that when someone protested, they were standing before others and declaring their thoughts. Throughout the centuries, the term developed a more oppositional connotation, and during the civil rights movement it finally evolved into its modern meaning of "mass demonstration".
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.