For readers who grew up with Harry Potter, the incantation "avada kedavra" is likely as burned into their skulls as Harry's lightning bolt scar. The Avada Kedavra inspires fear in the Harry Potter series since the curse can kill people quickly, and it's completely unavoidable with other protective spells. However, while all Harry Potter fans are intimately aware of the words used to cast the killing curse, they are likely not sure exactly where it comes from. To be fair, while author J.K. Rowling has offered her own explanation for the phrase, even some etymologists would take issue with the spell's true origin.
Source：https://www.cbr.com/what-avada-kedavra-means-harry-potter/
