The first use of the word rival in fifteenth-century English was with the now-extinct definition of "shore" or "bank". That, through Old French rivaille, comes from the Latin noun rivus, meaning "small stream". The current meaning of rival developed through Latin rivalis, which meant "person who fishes alongside another person". Originally, this implied friendly company, but eventually grew to have a sense of "one who competes for fish", and, by the 1570s, the term was extended to people competing in any field. Rivus is reconstructed as deriving from the Proto-Indo-European reconstruction her, meaning "to move" or "stir". The modern verb came about circa 1600, the adjective dates from the 1580s, and usage of rival has been steadily declining since a peak in 1780.
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.