The word "adieu" originates from the French language, where it literally means "to God". Over time, it has been adopted into English and other languages, retaining its sense of formal farewell or parting. The context of using "adieu" is typically more formal or ceremonial compared to casual interactions. It's often used in situations where there is a sense of finality, such as when someone is leaving for a long journey, relocating permanently, or in more solemn farewells.