This Spell In Harry Potter Was Named After A Greek Myth
Since the late '90s, the "Harry Potter" universe — consisting of books, movies, stage productions, and all manner of merchandise — has been a part of the popular culture, particularly in English-speaking nations like the U.S. and Harry's home, the U.K. The books draw on multiple sources for their inspiration, from people who were important in author J.K. Rowling's life, to the mundane realities of growing up in the British educational system.
However, the more fantastical elements of the story come from sources that Rowling could have expected her readers to have at least some familiarity with: the folklore of Western Europe and the British Isles. Werewolves, thestrals, and other folkloric creatures pop up in the narrative, and words, phrases, spells, and other situations will come up from time to time that astute historians will recognize as referencing, for example, some bit of European folklore or, in many cases, a reference to Greek mythology.
This spell references a creature from Greek myth
For those not familiar (and indeed, some pretty major spoilers are about to follow), in "Harry Potter and the Order of the Phoenix," Harry and his friends resort to a bit of trickery in order to hold secret meetings of Dumbledore's Army without being noticed by their teachers or by kids who would snitch on them. Specifically, according to Screen Rant, each person was given a fake coin that would transfigure whenever Harry manipulated a master coin that controlled the others. The entire process was known as the Protean Charm, and it was suggested by Harry's gifted friend, Hermione Granger.
According to GreekMythology.com, the actual Proteus was himself a shape-shifter. Blessed with the ability to provide information about the past, present, or future to anyone who asked, Proteus eventually took to using his shape-shifting abilities in order to get away from being continually pestered. To this day, the word "protean" remains in English, and refers to anything that can change form frequently or easily.