Adieu (pronounced “ah-DYOO”) is a formal French word meaning goodbye, but it carries a weightier sense than a casual “see you later.” When you say adieu to someone, you're acknowledging that you might not see them again for a very long time, or perhaps ever.

The word comes from a French phrase meaning “to God,” reflecting the idea of entrusting someone to God's care when parting. In old novels and movies, characters often bid each other adieu before long journeys or dangerous adventures. A soldier might say adieu to his family before sailing to war, or an explorer might bid adieu to her homeland before a years-long expedition.

Today, English speakers rarely use adieu in everyday conversation. It sounds old-fashioned and dramatic. You wouldn't say adieu to your friend at the end of the school day. But you might encounter it in classic books, historical films, or when someone wants to sound particularly formal or dramatic about a farewell. Some people use it playfully, giving extra weight to an ordinary goodbye, though this can sound affected or silly if overdone.