The first grammatical apostrophe (') only originated five hundred years ago, when early Renaissance writers started using them to contract words. For the next several centuries, it grew increasingly popular, but without standardized usages (this is why Shakespearean writing has unusual and often inappropriate-seeming apostrophes cleaving words in half). To complicate matters, a few centuries after its introduction, somebody thought to use it to indicate possessives as well. Eventually grammar grew more standard and people began using apostrophes as we know them today, but for a few hundred years it was a right kerfuffle. But why do we call it an apostrophe anyway? Isn't that also a word for a rhetorical device when a character addresses an absent person or object? Well, through Latin, both of those words come from the Ancient Greek verb apostrephein, meaning "to turn away". The little hook in the punctuation mark turns away, and an actor turns away when dramatically addressing an imaginary entity. Beyond that, the etymology is unknown, but it's probably from a Proto-Indo-European word also meaning "turn".
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd